electrical drain

[hughscpa]

I am working on the sheriff's m1113 and have run into a problem. The batteries drain over night. I have disconnected the negative from both batteries to stop it but what is wrong? with the front battery hooked up as it should be and the neg off on the second battery, I can flip the start switch to run and the brake light comes on and the wipers will run. no hornbut I think the heater fan also runs. Is this normal and I need to look elsewhere or is something hooked up wrong. I was going to put in a battery disconnect switch but with this situation would I need two?

 

[ctmustang]

If it has that serious of a drain its a problem that needs to be fixed. Without a wiring diagram in front of me its hard to say but id start with a schematic and see where the things you listed share power source etc. No battery disconnect- may in time end up on the road in a blaze of glory. Wiring is a ***** but if you take your time you should be able to trace it down.
CT

 

[ClarkeF]

About the only thing in a base HMMWV that can pull power when the truck is off is the KDS box under the dash, and the lights.

To start, I would charge the batteries. Put a digital AMP meter in series with the negative post on the rear battery to the shunt (disconnecting the heavy cable). What is the reading in amps or milliamps? It take a few minutes for the KDS box to go to sleep - so make sure you haven't moved the ignition to run before doing this or wait for it to time out. (needless to say you can fry your meter if you try and start the truck with the meter inline).

If you have more than a few milliamps of current, I would unscrew the connector from the back of the light switch - did the current go away? that's your problem. Disconnect the meter. Remove the connector to the KDS box. reconnect the meter - any current? If you had current before but don't now, that's your likely culprit. Still have current with the KDS and light switch disconnected? Any radios? A/C? Once you find the source of the parasitic drain the current will drop to 0 and you know what to fix.

DO NOT disconnect the KDS box without first disconnecting the battery. If you do disconnect it with batterys attached, you may be buying a new one.

Cheers,

Clarke

 

[Darwin T]

this won't fix the problem but it will stop the battery drain. PriorityStart 24-Volt ProMax. when the battery get to a point where it only has enought power to start it turns off and saves that power. i have not used one, but, i just installed one yesterday. if you leave you lights on or have a power drain of any kind it is suspose to save you.

you still need to find the power drain.

 

[hughscpa]

Another thing it does right after starting is that the voltmeter will drop into the yellow about 5 or 8 times. You can here a definate change in the draw on the engine. It is as if something is drawing power and cycling. Could that be the PCB also? Mine is a Prestolite.
Thanks,
Hugh

 

[ctmustang]

I have seen a couple alternators over the years actually be a draw-figure that one

 

[135gmc]

See if you can borrow a DC clamp-on ammeter and see what's pulling power when you're shut down - you could have a shorted diode in the alternator.

 

[emmado22]

Make friends with the local National Guard maintainece unit.. M1113's are totally different beasts than the M998 series.

 

[jwaller]

Another thing it does right after starting is that the voltmeter will drop into the yellow about 5 or 8 times. You can here a definate change in the draw on the engine. It is as if something is drawing power and cycling. Could that be the PCB also? Mine is a Prestolite.
Thanks,
Hugh

this is normal. what you are seeing is the after start glow plug cycle.

 

[hughscpa]

At least one less thing to try and figure out.