Dead electrical power in M925

[Karl kostman]

Hello folks I find myself in need of some thoughts please. I have a 1985 M925A1 and the truck has been 100 % problem free for years or until this week. I parked the truck in my warehouse last Nov. and went to fire it up this week, the batteries had been on a maintainer the entire time and they are both over 12 volts. Well when I hit the battery switch in the truck absolutely nothing happens, no lights absolutely nothing. I went over all the battery connections so they are clean and tight, the battery switch test out just fine I disconnected and reconnected all the circuit breakers and still nothing. I have power up to the Protection box on the firewall in front of the driver under the hood but the truck is a stone right now. I have never had one of those protection boxes go bad before, are these symptoms of that box being dead? If you have thoughts on what else I should check please let me know and I thank you for your suggestions and thoughts!
Karl

 

[NDT]

Do the batteries pass a load test? Sometimes the maintainers are maintaining a battery that is shot.

 

[Mullaney]

Hello folks I find myself in need of some thoughts please. I have a 1985 M925A1 and the truck has been 100 % problem free for years or until this week. I parked the truck in my warehouse last Nov. and went to fire it up this week, the batteries had been on a maintainer the entire time and they are both over 12 volts. Well when I hit the battery switch in the truck absolutely nothing happens, no lights absolutely nothing. I went over all the battery connections so they are clean and tight, the battery switch test out just fine I disconnected and reconnected all the circuit breakers and still nothing. I have power up to the Protection box on the firewall in front of the driver under the hood but the truck is a stone right now. I have never had one of those protection boxes go bad before, are these symptoms of that box being dead? If you have thoughts on what else I should check please let me know and I thank you for your suggestions and thoughts!
Karl

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It might be worth cracking open the cover on the Protection Box and verify that the "guts" aren't corroded. While I was posting this @NDT mentioned verifying the batteries. I had thought about mentioning checking the water level in the batteries - so same idea...

 

[Jbulach]

Karl, check out post #21 and #26 in this thread.

Ever see inside the Protective Control Box?

I had a failure of the PCB in my M925A1 last year. As part of the troubleshooting, I made some notes and took some pictures, attached. Mine was the type with a circuitboard. Hopefully the wiring diagrams will be helpful to someone in troubleshooting. I also put together a little...

www.steelsoldiers.com

If you try this, do not remove the jumper between C&D while the engine is running, it will have the same effect as turning your battery switch off before the start/run switch.

 

[Karl kostman]

Thanks much for the information guys, I load tested the batteries a year ago but will do that before I go any further. Thanks again for the assist in this adventure!

 

[Shirehorse]

I echo all the above advice with the protective control box, but wanted to mention something else.

Another area of issue with the electrical system is the STE/ICE test port on the passenger side. It corrodes around the connector and will eventually short out. Sometimes that takes the form of letting the magic smoke out, and sometimes it takes the form of a parasitic drain. Worth a look and a removal if you don't need STE/ICE functionality.