Electrical failure

[scottmh]

This morning I was driving my m109a4 to work and had a electrical failure. At 50mph I lost power. Coasted into a gas station. When the accessories switch is switch on something clicks and the gauges jump but then go dead. Start switch does nothing. Headlights and other lights work but that's it. Towed it home and got a ride to work. Is there a relay behind the dash that controls the gauge panel and in turn something that controls running?

 

[scottmh]

Also I did feel around the switches for a loose connection but did not locate any

 

[Valence]

I probably know the least out of anyone here, so I'm just guessing and what I say is less than a grain of salt - but isn't the only electrical part needed to keep the engine running the fuel pump? Could that be why you lost power?

 

[scottmh]

When it happened it was a definite loss of power. At first I thought my throttle cable broke. It was still running but almost as if you rook your foot of the pedal. It down shifted and I was loosing speed so I pulled into a gas station when the truck stopped the motor killed. I jumped out and checked to make sure I wasn't empty. I flipped the accessories switch off and on noticing the twitch in the gauges and the click behind the dash. With the accessories switch on the start switch does nothing. I guess it could be the fuel pump but then why would the gauges not read. Also with the accessories switch on the clicking and twitching is periodic. Almost like a relay trying to engage.

 

[LowTech]

Loss of electric shouldn't affect the engine. I ran for a week w/ a bad alt. I'd jump it off the She Beast (109) and drive for most of the day till the turn signals wouldn't flash, then charge some more. The only thing that I know is running on the electric while running is the in tank pump and the lights, etc.
So if the engine died I'd think it was one of the two needed to run, Fuel + air.

 

[scottmh]

On my truck I have always turned the engine off by switching the accessories switch to off. I opened up and I'm pretty sure I have a bad switch and a short on a wire labeled 27 going to the accessories switch. Time to break out the wiring diagram

 

[LowTech]

Going back I see that you have an A4, ours is an A3 and I may not know what I'm talking about when it comes to your engine setup.

 

[welldigger]

M35a3's and m109a4's WILL shut down with a catastrophic loss of electrical power. They have a shut off solenoid.

To your problem, I bet you have a short somewhere. Check anywhere a wire passes through or near the frame and firewall first. Then keep looking if you don't see anything.

 

[scottmh]

Unfortunately I am out of town so finding the offending circuit will have to wait until next weekend

 

[welldigger]

One more hint to locating your short. You said you heard a clicking noise. That is usually the circuit breaker in the 3 lever light switch tripping. Another sign of a short.

 

[scottmh]

Update! The wire labeled 1 (field wire)on the alternator shorted and was causing the problem. Because I've had alternator problems for a while I decided to disconnect the wires and tape them up.

 

[Jeepsinker]

Glad you got it figured out.

 

[scottmh]

Yeah now I need to get off my butt and get the 27si conversion in the works. Too many projects haha