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Diagnostic help please.

1K views 14 replies 5 participants last post by  madpogue 
#1 ·
Hi all, I need some help diagnosing a battery drain problem or short. I pressure washed the outside of the truck only, not the engine compartment, and when I went to move the truck the next day batteries were dead. Long story short, they wouldn't hold a charge so I bought 2 new batteries. All good I thought but by the next morning they were dead.

There is a definite draw on the battery (the light on the hood is disconnected). I hooked the battery up to the positive terminal and put a test light in between the negative post and the ground cable and it is lit bright. I pulled every fuse in the cab and engine compartment one by one. Light never went out. I disconnected the starter, light still on. I pulled and disconnected both tail lights, head lights, still nothing. I am at a loss. It is clearly connected to my pressure washing but I have no idea what is causing the short or how it is not tied to a fuse.

1996 7.3

Thanks for any help or ideas.
 
#2 ·
Sounds like water got into a connector, possibly the trailer or plow connector? Light on somewhere? Was the hood open? Did you pressure wash the underside? Might be a long shot, but is there a light in the glove compartment? I left mine on a couple of times in vehicles and it killed the battery.
 
#6 ·
I once knew an old mechanic for whom I had a lot of respect. He told me of a trick he used to find hidden shorts. Take a compass and move it around suspected areas. When you get close to the short, the needle will react by pointing to the short. I HAVE NEVER TRIED IT... only because I've never had occasion. I know there are lots of crafty folks here, maybe someone has tried this?
Also, the starter relay is a power distribution point, maybe play around in this area to isolate the issue. Good luck!
 
#8 ·
I would be looking for something with a direct connection to the battery. Something like your power distribution box or possibly a starter relay or the starter itself. If you've pulled all the fuses then your drain is coming before the fuses get power. Maybe even the alternator? It should have a connection directly to the battery
 
#10 ·
Thanks for the help everyone

Turned out to be a completely shot starter relay. Just coincidence that it went when I was pressure washing it, I guess. It tested bad and then actually started smoking. I ordered a Stancor relay from Diesel Orings.

Thanks for the diagnostic help everyone.
 
#12 · (Edited)
The starter was not cranking but would if I turned on the ignition. The problem I found was that the short was clearly linked to the GPR because when I pulled the hot wire to the GPR from the battery my draw stopped (and it was strong). With the GPR hot wire connected both terminals (large) showed 12v, without the key on. The glow plug relay side should not have any volts until the key is engaged (at least that is my understanding). I did not check the pcm wire. When I hook up the stancor relay is not the PCM wire the ground wire? Does the stock relay ground to the mount?
 
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