M923A2 electrical gremlins multiple gauges and CTIS not working one caught fire!

[337Armory]

Hey everybody new to the forum and MVs. I bought an M923A2 and everything worked fine. One day I went to drive it and the fuel gauge had pegged. Later that day I saw a spark behind the tach and all power to the truck cut out and I coasted to a stop. After a few minutes and flipping the switches a few times it started back up and made it home. I drove it again the next day but the switches were acting like they did when it cut off on me after flipping them repeatedly it started. The first day it started acting up we had got a lot of rain ALOT! That is why I kept driving the truck to see if it was part of the problem. Drove it again the next morning and the engine temp gauge caught fire right behind the glass. It was at this point that the CTIS lights started blinking in random patterns until I unhooked the connector. As of now the fuel gauge isn't working (it has tested bad) (the sending unit tested good). The engine temp gauge that caught fire is bad. The oil pressure gauge isn't working (sending unit good). The ABS light now stays on. The CTIS tests power at the plug but the lights are not coming on. The over speed light no longer works for some reason. I know that the gauges will have to be replaced but what worries me is why they all fried. Does anyone think the black box might have something to do with it? No one in my area knows anything about these trucks and neither do I. Any help would be welcomed and greatly appreciated. Thank you Lee

 

[Csm Davis]

Okay what is your voltage? Check it with a meter sounds like a truck I just picked up that the gages exploded in, due to a over voltage problem. I believe that the quick jump at drmo fried the voltage regulator which caused the problem. Just in case anyone doesn't know, you should let any truck you are slaving off charge for 5 minutes before you crank it and I let them charge for a few minutes after it is running to help the batteries back up to a good charge so the dead trucks alternator doesn't fry.

 

[337Armory]

I had it at my friends shop and he said the voltage was ok. The voltage meter and air pressure are the only gauges that are working. I have never had to jump the truck off or jump off another truck using mine. Thank you so much for your response. Any other ideas?

 

[CBR Metalworks]

Over speed light will not work when CTIS is unplugged, the CTIS not working is probably something different (I am surprised it worked before!). The PCB is likely bad, no guarantees it is causing the sparking problems behind the dash, but from what I saw that day at the gun show it displays all the symptoms of a bad PCB (no power at dash panel, or sometimes it works sometimes not). The dash on the 939 series trucks are a pain to remove, but it must be removed to replace the gauges anyways, so I would start with removing the dash and checking all the wiring.

Like Jeff mentioned, check and see what it is charging at with a voltmeter (the one on the truck does not count). I don't think that is your problem but it is a good thing to check. Water dripping down behind the dash MIGHT cause issues, but the connectors and gauges seem fairly robust/watertight from what I have seen, and aside from being submerged in water I don't think a few drips would affect much (now rust/corrosion caused by water might though).

#1 thing you need to start with is a new (or used) PCB (black box). You could have a loose connection elsewhere causing the truck to shut down and/or not start, but the contacts in the PCB commonly go bad and are likely part of the problem (if not 100% of the problem)

 

[wheelspinner]

Need to check the ground of your protective control box. It is grounded through the bottom right stud as you face the box from under the hood. There can be NO paint on ANY of the surfaces. Including the little spacer slugs. Start there.

 

[5tonman1971]

If they cuaght fire your voltage regulator is not functioning properly it may be an intermittent issue cuassing your buddy to get a false reading