wiring problems with 743 bobcat

[billrbg]

It might take a while but it sounds like this process has already taken a lot of time, but here is my idea to find it. disconnect one wire at a time ( like the alternator) run the machine and see if that changed anything. If it did, you found your problem. If it did nothing to help, put the wire back where it belongs and move to another wire to try. If the diode is bad or missing, it will back-feed, that in my opinion is the best one to start with. When it starts, does the starter disengage for a second or two then re-engage after it starts? If it does, that to me sounds like there could be power coming back after the alternator energizes and starts charging. However, if the starter never does disengage from the time you turn the key and stays engaged after the eng is running, it's probably something else, like a stuck solenoid or stuck starter drive.

OP, where are you located? Maybe there IS somebody close enough to come help. Didn't you already try disconnecting the starter solenoid from the harness and start it with a jumper between the small and large terminals on the solenoid; doesn't it start and run fine like that? That would prove that it is *only* an electrical problem elsewhere, no problem (either mechanical or electrical) with the starter itself. You confirmed that it isn't a 743B, but what about a 743DS? That would have a separate placard near the P/N - S/N one that reads "UL approval of DS rating for... ". The cab schematic for the 743 and 743DS is the same, but the engine schematic is different.

 

[mark18mwm]

OP, where are you located? Maybe there IS somebody close enough to come help. Didn't you already try disconnecting the starter solenoid from the harness and start it with a jumper between the small and large terminals on the solenoid; doesn't it start and run fine like that? That would prove that it is *only* an electrical problem elsewhere, no problem (either mechanical or electrical) with the starter itself. You confirmed that it isn't a 743B, but what about a 743DS? That would have a separate placard near the P/N - S/N one that reads "UL approval of DS rating for... ". The cab schematic for the 743 and 743DS is the same, but the engine schematic is different.

Yes billrbg is right. disconnect the small wire going to the solenoid. Start it with a jumper or even a screwdriver or any piece of metal by touching that small wire terminal to the big battery terminal, it will turn over and start so keep your self clear so nothing grabs you or runs you over. Once it's running, see if the starter is still engaged, if it is it is a starter problem. if not it is electric, like he said. Also, while it is running, put a test light or meter on that small wire ( while it is off the starter) and se if it has power, it should not. It should only have power when the key is turned to "start" NOT when turned to "run". If it does, you have power coming from someplace that it shouldn't be, like I said in the previous post, the hard part is finding out where.

 

[superniceguy5687]

Yes billrbg is right. disconnect the small wire going to the solenoid. Start it with a jumper or even a screwdriver or any piece of metal by touching that small wire terminal to the big battery terminal, it will turn over and start so keep your self clear so nothing grabs you or runs you over. Once it's running, see if the starter is still engaged, if it is it is a starter problem. if not it is electric, like he said. Also, while it is running, put a test light or meter on that small wire ( while it is off the starter) and se if it has power, it should not. It should only have power when the key is turned to "start" NOT when turned to "run". If it does, you have power coming from someplace that it shouldn't be, like I said in the previous post, the hard part is finding out where.

Hi everyone. Thank you very much for the information. It seemed to crank when I shorted out the starter. It seemed to disengage when I was cranking it that way. Just like a car would when it doesn't start and you keep trying to start it over and.over. I will try the removing of wires one by one and see what happens. I live up here in Canada, in Saskatchewan. If I did start it and it is running should I test light the hour meter wire back wards. Or should I just have key on? There is two connectors on the hour meter. One by the looks of it has battery power to one side then the ignition to the other. No it isn't a DS. Just a straight 743. I followed the schematics in the service manual. Some of the models are identical except for a couple of them.Once again thank you for the posts. I am super busy but will try the suggestions and re post as soon as I can.

 

[mark18mwm]

Hi everyone. Thank you very much for the information. It seemed to crank when I shorted out the starter. It seemed to disengage when I was cranking it that way. Just like a car would when it doesn't start and you keep trying to start it over and.over. I will try the removing of wires one by one and see what happens. I live up here in Canada, in Saskatchewan. If I did start it and it is running should I test light the hour meter wire back wards. Or should I just have key on? There is two connectors on the hour meter. One by the looks of it has battery power to one side then the ignition to the other. No it isn't a DS. Just a straight 743. I followed the schematics in the service manual. Some of the models are identical except for a couple of them.Once again thank you for the posts. I am super busy but will try the suggestions and re post as soon as I can.

If the hour meter has two leads and one is battery power and one is ignition, that is one problem. That might also make it back feed power. The two leads are one for + to the ignition to give power ONLY when the key is in the run position. The other lead - is for ground. If you are running battery power to the hour meter it will surely be feeding the ignition circuit with the engine off. start by checking that. Make sure one (the+) goes to the ignition and the (-ground) terminal is grounded to the frame or engine. I'm not certain that is the entire problem, but if it is as you say bat to one and ign to the other, it is wrong.

 

[superniceguy5687]

If the hour meter has two leads and one is battery power and one is ignition, that is one problem. That might also make it back feed power. The two leads are one for + to the ignition to give power ONLY when the key is in the run position. The other lead - is for ground. If you are running battery power to the hour meter it will surely be feeding the ignition circuit with the engine off. start by checking that. Make sure one (the+) goes to the ignition and the (-ground) terminal is grounded to the frame or engine. I'm not certain that is the entire problem, but if it is as you say bat to one and ign to the other, it is wrong.

Hi everyone: Well I finally got back to the bobcat. This is what I have found so far. The hour meter as a red wire to the batt side of it. The other wire is a yellow wire with brown strip, to the other terminal. Seems like the other end goes to a charge pressure fitting. It isn't black , going straight to ground. Seems like it goes to a charge pressure, sensor? That's what the wiring diagram seems to say. As far as the ignition switch, have the white wire going to center terminal, Orange to ignition terminal, red to batt terminal, and blue with black strip to the accessories? This was according to the wiring diagram. Does this sound right? I looked at the serial number plate and there was nothing saying anything about a DS model or, anything like that. I was wondering if the pinion gear from the starter, was getting wedged into the ring gear teeth at all? What would be the easiest, approach to check if the gears are lining up properly? Do I just count the number, of teeth on the starter gear per inch and then count the ring gear per inch? Looked at all of the other wires, nothing got damaged insulation wise when I put the harness in so nothing is shorting out that way. Triple checked the relay wires and seems to be right according to the schematics.

 

[billrbg]

Hi everyone: Well I finally got back to the bobcat. This is what I have found so far. The hour meter as a red wire to the batt side of it. The other wire is a yellow wire with brown strip, to the other terminal. Seems like the other end goes to a charge pressure fitting. It isn't black , going straight to ground. Seems like it goes to a charge pressure, sensor? That's what the wiring diagram seems to say. As far as the ignition switch, have the white wire going to center terminal, Orange to ignition terminal, red to batt terminal, and blue with black strip to the accessories? This was according to the wiring diagram. Does this sound right? I looked at the serial number plate and there was nothing saying anything about a DS model or, anything like that. I was wondering if the pinion gear from the starter, was getting wedged into the ring gear teeth at all? What would be the easiest, approach to check if the gears are lining up properly? Do I just count the number, of teeth on the starter gear per inch and then count the ring gear per inch? Looked at all of the other wires, nothing got damaged insulation wise when I put the harness in so nothing is shorting out that way. Triple checked the relay wires and seems to be right according to the schematics.

Can somebody post a schematic in this thread that we can refer to? I have one, but can't do attachments; I would have to email it to somebody else to post.

 

[Tazza]

Can somebody post a schematic in this thread that we can refer to? I have one, but can't do attachments; I would have to email it to somebody else to post.

The hor meter goes through the pressure sender as just in case you left the switch on it will not keep ticking over. No hydraulic pressure means the machine is not running, so the hour meter stays off.

 

[billrbg]

The hor meter goes through the pressure sender as just in case you left the switch on it will not keep ticking over. No hydraulic pressure means the machine is not running, so the hour meter stays off.

Aren't we wandering in circles here? The below would indicate the starter itself is fine, this is all a wiring issue: "Hi everyone. Thank you very much for the information. It seemed to crank when I shorted out the starter. It seemed to disengage when I was cranking it that way." Again, if you can crank it by "hot wiring" right at the starter solenoid it should start and run fine. You can try that over-and-over until you are confident the starter dis-engages properly if controlled properly by the electricals. With all electrical except the starter disconnected, you may not be charging the battery, and it will probably be harder to start because of no glow-plugs available, but let's get past wonderment about whether it is a mechanical or electrical problem.

 

[superniceguy5687]

Aren't we wandering in circles here? The below would indicate the starter itself is fine, this is all a wiring issue: "Hi everyone. Thank you very much for the information. It seemed to crank when I shorted out the starter. It seemed to disengage when I was cranking it that way." Again, if you can crank it by "hot wiring" right at the starter solenoid it should start and run fine. You can try that over-and-over until you are confident the starter dis-engages properly if controlled properly by the electricals. With all electrical except the starter disconnected, you may not be charging the battery, and it will probably be harder to start because of no glow-plugs available, but let's get past wonderment about whether it is a mechanical or electrical problem.

Hello. Sorry to get you upset bill. There is a lot of over and over and I apologize for that. It's just crazy that's all. I mean its not the wiring system like in a car or a semi truck. I know that what seems logical, also has come to fail on this machine. It would be nice just to get down to the root of these problems and just be able to hop in ,glow it and fire it up with out this starter wanting to have a mind of its own and still try to start the engine just after it just fires up. Just like when I turn the key and take my hand off the key to switch it back over to glow I can get out of the machine and it will still keep cranking without me even turning the key. Also sorry to disappoint , you too Tazza. But even when it was working before the fire that is, I would turn the ignition switch to the middle position, and pull up on the shut off to stop the engine, the engine did quit but then a couple seconds later the hour meter would start up and start ticking away as if the engine was still running, and it wouldn't stop till I took the battery cable off. Weird thing, still does all of that with all of the new stuff. When I do start cranking and after a couple times , It will keep cranking even when I am not in the machine and the key is in the run position, the only way I can get it stop cranking is by pulling the cable off of the battery. I am very appreciate of all of the help everyone has given . I hope that this doesn't start happening to someone else. I am going to get to root of the problem, and am not about to give up. Hope everyone is doing well.

 

[mark18mwm]

Hello. Sorry to get you upset bill. There is a lot of over and over and I apologize for that. It's just crazy that's all. I mean its not the wiring system like in a car or a semi truck. I know that what seems logical, also has come to fail on this machine. It would be nice just to get down to the root of these problems and just be able to hop in ,glow it and fire it up with out this starter wanting to have a mind of its own and still try to start the engine just after it just fires up. Just like when I turn the key and take my hand off the key to switch it back over to glow I can get out of the machine and it will still keep cranking without me even turning the key. Also sorry to disappoint , you too Tazza. But even when it was working before the fire that is, I would turn the ignition switch to the middle position, and pull up on the shut off to stop the engine, the engine did quit but then a couple seconds later the hour meter would start up and start ticking away as if the engine was still running, and it wouldn't stop till I took the battery cable off. Weird thing, still does all of that with all of the new stuff. When I do start cranking and after a couple times , It will keep cranking even when I am not in the machine and the key is in the run position, the only way I can get it stop cranking is by pulling the cable off of the battery. I am very appreciate of all of the help everyone has given . I hope that this doesn't start happening to someone else. I am going to get to root of the problem, and am not about to give up. Hope everyone is doing well.

Does the small wire terminal have power to it when it takes off cranking on it's own? If that terminal only has power when the key is turned, then the wiring should be right but possibly the solenoid it self is sticking. If that wire has power constantly the starter will continue to engage and turn the engine over. If you are desperate to use the machine, you could put a momentary contact switch like a push button, in line so it only has power when you push the button. That is cobbling I admit, and doesn't fix the real issue but until you find the real problem it might let you still use the machine. I still think you are getting a back feed of power from somewhere. You say you know you have something wrong with the hour meter, try to disconnect the hour meter and see if that helps it crank normal. After that I would try to start it with out the alternator connected, see if that helps or not. I guess after that I would look at the wiring harness at the key switch and make sure it's assembled properly, with the right wires in the right locations in the plug in, they are assembled by hand and factories have made mistakes before. Just some ideas, good luck.

 

[billrbg]

Does the small wire terminal have power to it when it takes off cranking on it's own? If that terminal only has power when the key is turned, then the wiring should be right but possibly the solenoid it self is sticking. If that wire has power constantly the starter will continue to engage and turn the engine over. If you are desperate to use the machine, you could put a momentary contact switch like a push button, in line so it only has power when you push the button. That is cobbling I admit, and doesn't fix the real issue but until you find the real problem it might let you still use the machine. I still think you are getting a back feed of power from somewhere. You say you know you have something wrong with the hour meter, try to disconnect the hour meter and see if that helps it crank normal. After that I would try to start it with out the alternator connected, see if that helps or not. I guess after that I would look at the wiring harness at the key switch and make sure it's assembled properly, with the right wires in the right locations in the plug in, they are assembled by hand and factories have made mistakes before. Just some ideas, good luck.

I am not upset, we are here to help each other. If a thread does start to annoy me, I'll just back away from it quietly. I am, however, confused! It still isn't clear to me if the starter "cranks by itself" when all wires are removed from the small stud on the solenoid; when there is NO possibility of there being voltage applied there. Yes or No, does it ever crank when there is no wire connected to that small solenoid stud?

 

[superniceguy5687]

I am not upset, we are here to help each other. If a thread does start to annoy me, I'll just back away from it quietly. I am, however, confused! It still isn't clear to me if the starter "cranks by itself" when all wires are removed from the small stud on the solenoid; when there is NO possibility of there being voltage applied there. Yes or No, does it ever crank when there is no wire connected to that small solenoid stud?

Hi everyone. I have been super busy lately and it is going to get worse for the next little while. The answer to the last post is no. When I have the small wire off on the starter , it doesn't seem too. When I short it out it seems to turn over the starter fine. When the little wire is back on to the starter, then it starts to do all the weird stuff. I am going to start disconnecting one thing at a time as one of the posts had mentioned. while trying to use the key. But the answer to your question billrgb is no. When the killed wire is not connected to the starter it seems okay. But as far as the hour that thing has a mind of its own. I also put a new one of those in too.

 

[superniceguy5687]

I am not upset, we are here to help each other. If a thread does start to annoy me, I'll just back away from it quietly. I am, however, confused! It still isn't clear to me if the starter "cranks by itself" when all wires are removed from the small stud on the solenoid; when there is NO possibility of there being voltage applied there. Yes or No, does it ever crank when there is no wire connected to that small solenoid stud?

Hi everyone. I have been super busy lately and it is going to get worse for the next little while.The answer to the question is no. When the little wire is off of the starter, and I hook my test light to that little wire it will light up and go out with the key. When I turn the key will light up. Turn the key off, the test light goes out . When when I go to short the lttle wire out to the starter it will crank. I take the little wire off off the starter it stops cranking.It seems to turn the starter fine this way.. When the little wire is attached back on too the starter, then it starts to do all the weird stuff. I am going to start disconnecting one thing at a time as one of the posts had mentioned. while trying to use the key and see what I can find out. But the answer to your question billrgb is no. When the little wire is not connected to the starter it seems okay. When the little wire is attached that is when things are not so good. That is when I am trying start it ,and you turn the key to start ,it will engage the starter, the starter will keep cranking after that, and even if I put the key in the middle,it will still keep turning over , then if the motor happens to start , even though the revs are low , you can still hear the starter turning over. The only way I make it stop is by pulling the positive cable off the battery. But as far as the hour meter that thing has a mind of its own. I also put a new one of those in too.

 

[billrbg]

Hi everyone. I have been super busy lately and it is going to get worse for the next little while.The answer to the question is no. When the little wire is off of the starter, and I hook my test light to that little wire it will light up and go out with the key. When I turn the key will light up. Turn the key off, the test light goes out . When when I go to short the lttle wire out to the starter it will crank. I take the little wire off off the starter it stops cranking.It seems to turn the starter fine this way.. When the little wire is attached back on too the starter, then it starts to do all the weird stuff. I am going to start disconnecting one thing at a time as one of the posts had mentioned. while trying to use the key and see what I can find out. But the answer to your question billrgb is no. When the little wire is not connected to the starter it seems okay. When the little wire is attached that is when things are not so good. That is when I am trying start it ,and you turn the key to start ,it will engage the starter, the starter will keep cranking after that, and even if I put the key in the middle,it will still keep turning over , then if the motor happens to start , even though the revs are low , you can still hear the starter turning over. The only way I make it stop is by pulling the positive cable off the battery. But as far as the hour meter that thing has a mind of its own. I also put a new one of those in too.

OK, good. I am now confident that the starter itself is fine, let's focus on the rest of the wiring. Do you have the electrical schematic on-hand for ready reference? As I recall, you do; but if not we need to get one in your hands so we can all be "reading from the same page". There is no use having you disconnect various wires, or make various meter readings, if we can't be sure you are going after the same wires we intend!

 

[superniceguy5687]

OK, good. I am now confident that the starter itself is fine, let's focus on the rest of the wiring. Do you have the electrical schematic on-hand for ready reference? As I recall, you do; but if not we need to get one in your hands so we can all be "reading from the same page". There is no use having you disconnect various wires, or make various meter readings, if we can't be sure you are going after the same wires we intend!

Good day sir: Yes I do have the schematics for the wiring. I got a copy of the service manual that does have them for the cab the middle and the engine one. I am using the ones which the star by the number. For example , 743*

 

[billrbg]

Good day sir: Yes I do have the schematics for the wiring. I got a copy of the service manual that does have them for the cab the middle and the engine one. I am using the ones which the star by the number. For example , 743*

Can you post those schematics here? I have a version of the 743 schematics, but they may vary from what you are looking at. I think it would help if I (and any others) can be looking at EXACTLY what you are as we try to talk this through.

 

[superniceguy5687]

Can you post those schematics here? I have a version of the 743 schematics, but they may vary from what you are looking at. I think it would help if I (and any others) can be looking at EXACTLY what you are as we try to talk this through.

Okay. I will try and scan them and see if I can get it loaded onto the site. I really appreciate all of the help from everyone who had replied to my post. Now hopefully I can get it scanned properly, and to get it onto the site.

 

[superniceguy5687]

Can you post those schematics here? I have a version of the 743 schematics, but they may vary from what you are looking at. I think it would help if I (and any others) can be looking at EXACTLY what you are as we try to talk this through.

 

[billrbg]

In my next post I will make some suggestions, but want you to note two things: 1) Your photos and my copy have minor differences in format, but seem to be the same schematic. I will be using my much-easier-to-read copy, but if I start referring to wire numbers or colors that don't seem to match what you have, let's talk about it and resolve! 2) I have been unable to use a "line feed" in this forum, so I can't separate my writing into proper paragraphs for easier reading. All I can do is apologize about that and beg your patience. In some cases I may just do serial posts, a paragraph in each.

 

[billrbg]

In my next post I will make some suggestions, but want you to note two things: 1) Your photos and my copy have minor differences in format, but seem to be the same schematic. I will be using my much-easier-to-read copy, but if I start referring to wire numbers or colors that don't seem to match what you have, let's talk about it and resolve! 2) I have been unable to use a "line feed" in this forum, so I can't separate my writing into proper paragraphs for easier reading. All I can do is apologize about that and beg your patience. In some cases I may just do serial posts, a paragraph in each.

Browsing through the thread, to refresh my memory, it occurred to me that there may be some confusion about what "solenoid" is being talked about. I propose that the one mounted to the top of the starter, with the big battery cable attached, be called the "solenoid". The two small ones, mounted up under the air filter, I would like to call "relays"; one for the starter and one for the glow-plugs. That is how they appear on my schematic: (16) is the "Pre-Heat Relay" and (17) is the "Start Relay". My understanding is that when wire 21S (WHT/L. GRN) is connected to the (starter) solenoid you have the "continued cranking problem". And, if 21S is disconnected, then you can jumper at the starter between the big power stud and the small stud (for 21S) and the engine will start and then run fine; no continued cranking (as long as you remove the jumper after it starts!). Is that all correct? If so, then reconnect wire 21S and disconnect Chassis Connector (4). Then try starting it with the jumper and see if it is OK. None of the electricals should work like that, no glow plugs, alternator charging, lights, etc. but it should start. We will be chasing this back one connector at a time. If it works OK with connector (4) disconnected, then I will have you reconnect that and disconnect Harness Connector (1) and try again... If it isn't OK with just (4) disconnected, then try with both (4) and (1) disconnected.