New Holland L785 Battery Shorted Out; now No Start, No Lights on Control Module

[st0ck1ng]

Background: Have a NH L785; while working had the battery hold down come loose, which allowed the battery to slide into the frame and short out. Initial symptoms were that the boom/bucket would lock out, seatbelt light would come on, resetting the seatbelt would turn the light off and bring boom/bucket back on line. Absolutely no other indications of a problem. In researching symptoms everything pointed to failed seat or seatbelt switch. Replaced both, no change, it had been a few days, so I checked battery for charge, 1.2v, this is when I found the battery up against the frame with both terminals literally melted away. New battery installed, had to jump the starter to get it off the work site, thankfully the boom/bucket were still stuck up in the air, or wouldn't have been able to get it off the site.

Issues found so far: Altenator burned out; replaced.

Additional Actions Taken: Replaced 15 amp, 6 amp breakers and starter relay,

Seat and seatbelt switches seem to be working properly, ie, light goes off when both activated

Problem: will not start from key, CAN start by jumping starter relay from battery, but no boom/bucket controls, also there are no lights at the logic module, could the logic module be compromised? Is there a way to run diagnostics on the logic module or do any testing that will help determine if it is the problem.

So far have not found any wiring that indicates a failure point.

Any help greatly appreciated.

Thank you

 

[billybob_81067]

You are simply not getting power to your ignition switch or out from it when in the on position. These skid steers are really simple in the electrical department. Pull the overhead console cover off and probe around with a test light to see if you have power coming up to your ignition switch. If not, then the main power wire is either open or not getting power to it. Check the circuit breakers on the right hand side of the machine. There is a starter relay mounted there where it picks up power if I remember correctly.

The "logic module" you speak of is basically just dummy lights that light up when pressure or temperature switches connect a ground.

 

[st0ck1ng]

You are simply not getting power to your ignition switch or out from it when in the on position. These skid steers are really simple in the electrical department. Pull the overhead console cover off and probe around with a test light to see if you have power coming up to your ignition switch. If not, then the main power wire is either open or not getting power to it. Check the circuit breakers on the right hand side of the machine. There is a starter relay mounted there where it picks up power if I remember correctly.

The "logic module" you speak of is basically just dummy lights that light up when pressure or temperature switches connect a ground.

Thank you for the reply. At original post, I had power to the switch. I am assuming I have "burned" out a wire somewhere in the loom. I ran a new hot to the switch and back to the relay, so am able to start, BUT, still no signal to the boom/bucket solenoids, so still trying to figure out why they are not working, which takes me back to the logic module. I really do not want to pull all the wiring, but it may come to that.

 

[billybob_81067]

Ok so I just went and did some google searching looking for a wiring diagram and came across the logic module you are referencing. My L785 does not have that at all. I thought you were talking about the display with the dummy lights that illuminate if you lose charge pressure or oil pressure, or the engine temp or hydraulic oil gets too hot. Someone must have taken off the logic module on my skid steer before I ever got it. I know it had two wires wire nutted together around the seat area when I got it and when I did some re-wiring on it I cut them off short and soldered them together to make a solid connection. I assumed that was for either a seat belt safety switch or a seat sensor switch, but it may have been for both and coming from that "logic module". My skid steer controls will work as long as the key is turned to the on position. They will lock out if I turn the ignition off.

So I guess disregard my previous post as the wiring on mine is going to be a bit different from yours!

 

[st0ck1ng]

Would you mind sending my a rough sketch (if possible) of your wiring. I am certain I have figured out how to rewire mine without compromising the safety component of the bucket/boom solenoids, but would like to see how yours was done.

Again thank you for your response and info.

 

[Rayhat]

There are at least five pins in my round Logic Module connector ,and I would say several more without looking. I cannot imagine bypassing it. There is a specific sequence of events, "Key in on position-seat switch activated through a diode in the seat switch wiring- ignition", and that's just to start the machine. If that sequence is not followed in order the machine will not even turn over. I have relocated the seat switches to just one switch on the upper instrument panel on my machine, not really bypassing them. To start my machine, I turn ignition key to Acc position, turn on seat switch illuminating idiot light and sending a reduced diode voltage reading to the Logic Module, turn key to start/run position to crank/start the engine. I feel there is a host of other parameters the Logic Module controls.

I'm not saying it can't be done. But in my opinion which isn't worth Jack-shit you would be an electrical Jedi Master to accomplish it.

 

[billybob_81067]

I just did some looking on Messick's parts catalog for the wiring schematic and think I figured out why mine was so simple to bypass. Mine must be before serial # 733332 and have the following wiring schematic. Only one seat switch and only one interlock valve on the hydraulics that stops both the lift and curl. Much simpler system than what you're dealing with.

 

[st0ck1ng]

Folks my apologies, did not realize I had submitted the same post twice.

Billybob, Rayhat, Jim A, thank you for the thoughts and guidance.

In the end, the link shows how I got past the logic model and retained the safety features.

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