Problems with BOSS and glow plugs 1993 753

[Halojonssan]

Hey!

Recently bought my first skid steer and when i got back home with it after several hours of driving it would not start. Was not so cold out -12c but i plugged in the block heater and it started fine after an hour so i could pull it off the trailer.

I started checking out if there was an issue with the glow plugs and i see they're getting a constant supply of power when the key is turned on. Went to trace the wire in wiring diagrams i have found online so i can see if the previous owner put the wire for activating the relay in the wrong place but i can only trace is to the BOSS controller and since there is'nt any pinout diagram for the BOSS controller i cannot see what wire is going from there to the key so i don't know how to find is to see if he has just wired it wrong. Previous owner put on lots of extra lights on the machine so the wiring is a mess and things seem to have been removed overtime. The BISC seems to be bypassed since i can start the machine standing outside it no problem. So what cable is going to the key for activating the glow plug relay? Does anyone have a pinout diagram for the BOSS Controller?

Also i knew when i bought it the hour meter was not working but i failed to realise none of the gauges in the lcd are working. When i turn it on i see all of the symbols and then it just looks like this (borrowed a picture but it's the same on mine). Could the boss interfer with the glowplugs in some odd way? I don't know what to do with the BOSS problem.. Auxiallary hydraulics is a must for me. I found this in the manual for the machine so looks like probably the boss box has some issues. I took apart all the connectors and cleaned them and fixed up all of the earths i saw but nothing came of that.

Machine works great but it doesn't feel great running it without any gauges at all. Everything works though except the glow plugs which i suspect are burnt out by now since he probably has ran it for long with them constantly getting power. It starts up real quick with it sitting in the warm garage and the seller kept it in a warm garage at all times so he probably never thought of it. I don't really know what to do about it just buying a new boss controller if you can even find one seems real expensive and i am not opposed to going all manual gauges and stuff if i can get everything working.

I have little to no experience wrenching on equipment but a lot of experience on cars.

 

[Bernie B]

Do you have the service manual? It would have the schematics my 853 would crank but not start track down the faults on the panel I replaced the shutdown relay and got my machine to start.
The boss module under the cab may have corroded terminals.
The shutdown relay is mounted by the boss.

 

[ZekeSkyree]

Found a copy posted here ...

http://ardiehl.de/Bobcat/753/Bobcat-753-Service-Manual.pdf

 

[KyMadMan]

Hey!

Recently bought my first skid steer and when i got back home with it after several hours of driving it would not start. Was not so cold out -12c but i plugged in the block heater and it started fine after an hour so i could pull it off the trailer.

I started checking out if there was an issue with the glow plugs and i see they're getting a constant supply of power when the key is turned on. Went to trace the wire in wiring diagrams i have found online so i can see if the previous owner put the wire for activating the relay in the wrong place but i can only trace is to the BOSS controller and since there is'nt any pinout diagram for the BOSS controller i cannot see what wire is going from there to the key so i don't know how to find is to see if he has just wired it wrong. Previous owner put on lots of extra lights on the machine so the wiring is a mess and things seem to have been removed overtime. The BISC seems to be bypassed since i can start the machine standing outside it no problem. So what cable is going to the key for activating the glow plug relay? Does anyone have a pinout diagram for the BOSS Controller?

Also i knew when i bought it the hour meter was not working but i failed to realise none of the gauges in the lcd are working. When i turn it on i see all of the symbols and then it just looks like this (borrowed a picture but it's the same on mine). Could the boss interfer with the glowplugs in some odd way? I don't know what to do with the BOSS problem.. Auxiallary hydraulics is a must for me. I found this in the manual for the machine so looks like probably the boss box has some issues. I took apart all the connectors and cleaned them and fixed up all of the earths i saw but nothing came of that.

Machine works great but it doesn't feel great running it without any gauges at all. Everything works though except the glow plugs which i suspect are burnt out by now since he probably has ran it for long with them constantly getting power. It starts up real quick with it sitting in the warm garage and the seller kept it in a warm garage at all times so he probably never thought of it. I don't really know what to do about it just buying a new boss controller if you can even find one seems real expensive and i am not opposed to going all manual gauges and stuff if i can get everything working.

I have little to no experience wrenching on equipment but a lot of experience on cars.

Halojonssan,​

Having just gone through something similar this past year let me pass this along.

The BOSS system can not be purchased from BobCat as it is no longer made.
You might find one used, but no guarantee it will work in your specific machine.
You can check all the sensors yourself to rule out a bad sensor issue.
There IS ONE company that will work on the BOSS system and they are very good. Had my BOSS repaired by them ln late 2025. Works like it's brand new (because most parts were replaced with new) and it comes with a full 1 YR warranty. Their name is isoscell and I've attached their card.

If you need values for any of the sensors let me know I should still have them. The issue of your glow plugs being wired are more than likely the result of a failing BOSS or sensor. Though I don't know of any sensor that would lock out the plugs.