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Discussion Starter #1 (Edited by Moderator)
Hey guys, I haven't been on here for quite a while but I've recently come across an issue that after searching threads has my head spinning with so many possibilities. I'll give you the short background:

Truck in signature. 2002 350. About 188,000 miles now.
Truck had trouble starting in cold weather even below 50°. I had my mechanic replace the glow plug relay and he also did the air intake heater at the same time which I now understand has nothing to do with cold weather starting but anyway.
Went camping and the truck would fire in upper 40° weather with a little bit of coercing but I could tell that what he did did not resolve the problem and I am sure I've got some glow plugs out if not all of them. I went through the summer without any issue starting it due to the warm weather. Weather cooled off a bit come September. I had my truck batteries drain completely in a matter of two hours while at a park. Mind you, it was still in the 70's. Got it jumped and ran just long enough to get home while I watched the lights fade. Parked the truck and replaced both batteries and alternator after getting it tested as bad. Also through on a new serpentine belt for good measure.
Truck was running great, took it to Moab for the weekend, drove a few other places not a hiccup. A couple days ago the weather turned quite cold and for giggles I went out to start the truck in mid 30° weather without it being plugged in. I kind of figured it wouldn't turn over but thought I would give it a try. It cranked and I could tell it was not going to fire. I didn't want to push it so only cranked it a couple times. I didn't need the truck that day so I shut it off and went to work in my other truck. I came home at the end of the day and went to unlock the truck and everything was completely dead. We're talking not even enough juice to get a click or even a dome light. I've been able to charge up the batteries (only if cables removed) from totally dead to be able to hold a charge with the cables off. However, once I throw the cables on and test the batteries I have less than 1 V reading. I checked all the fuses I can find and everything looks fine. My gut is telling me that the glow plug relay or something associated has a short and is killing the batteries and drawing the power but there are quite a few other items that people mention that I need to know the best place to begin. Wiring to the relay looks fine but curious is the relay can get stuck in the "open"� position and always draw power.
Anyway, any help would be appreciated as I love my truck and need to get my butt out of this GMC run around!
Thanks
 

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Discussion Starter #2
Missed my main question. ? Curious if after shutting it off if the glow plug relay or something else could have stuck open and continued to draw power since two short cranks shouldn’t have completely killed the batteries.

Oh and sorry about the weird symbols in the text. I dictated the original post and something whacky happened!
 

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I’m afraid I’m not going to be a lot of help, but- if you’re suspecting the GPR circuit you could disconnect the 12V power to the relay, tape off the end of the wire (power) with some electrical tape, and then hook up your charger to your batteries to see if they will charge, isolating the gpr circuit. Plug in your block heater- and after batteries are fully charged- see if truck starts and doesn’t have the power drain anymore.
 

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I had a similar issue with batteries draining fast, but it had nothing to do with the ambient temperature. After sitting overnight, or even just for a few hours, the batteries would drain inexplicably - one battery drained so far that it could not be recharged. One day I went out to my shop where it is parked and noticed a faint clicking noise, which was coming from the headlight switch. In order to be sure that was the problem, I removed the headlight switch, recharged the one good battery and added a different one, then drove for a while with no headlight switch. My truck is not my daily driver, so obviously, if you have to drive at night, this would not be a good way to diagnose the problem!

Anyway, everything seemed to be fine, so I bought a new Borg Warner HL140 switch from Ama-you-know where. There is a lot of variation in the prices of headlight switches, from the Dormans on the low end to Motorcraft on the high end, I went for the mid range one. Ever since I removed the apparently defective switch, I've had no battery drainage issue.

Just a suggestion as something you might look at, or FWIW. I tried searching this forum for anyone else who has experienced a battery drainage problem from a defective headlight switch and it appears I may be the only one, and if your problem is temperature related as you seem to believe, this will not help you.

If you do decide to remove your headlight switch, search the forum on how to do it. There is a special way to remove it, by taking the knob off, replacing it 180 degrees, and turning backwards (or something like that) that releases the latches holding the switch into the dash.

Good luck!
 

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There's a distinct possibility that the replacement alternator you got was bad out of the box. If the diodes in the alternator go bad, they'll drain the batteries post haste. That's because the alternator then tries acting like a motor attempting to turn the serp belt. Disconnecting the main charge wire on the alternator and checking to see if the batteries discharge will confirm or eliminate the alternator, similar to what Big Horn suggested to check the glow plug relay, although if the GPR was stuck closed (on position), you'd likely draw a spark at the input connection as you disconnected it.

I fixed the weird symbols in your post. Sounds like your voice to text function can't handle apostrophes or quotation marks very well.

BTW, your signature isn't showing up. Don't know why that would happen. Things look OK in your profile. Maybe it's because you're using a smartphone to post.
 

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Discussion Starter #6
Thank you everyone. I ran through testing glow plug relay, alternator, even removing the starter and testing it. All checked out fine. Put back together and the truck is running great. I plugged it in last night and of course fired right up. I think my next step is to pull the valve covers and test the plugs and wiring harness. On a side note, my vacuum pump runs constantly so I have a leak somewhere there in that system. Can’t be good to run constantly. Maybe adding to draining the batteries or taxing the alternator?
 

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I had an alternator that would kill both batterys in a few hours but only did it occasionally. I went out one day after it sat a few hours and the alternator was too hot to touch but the engine was cold. Rebuilders cant test for that. It may have been sold many times and returned for warranty and then resold again after it passed charging tests.
 

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Look at the air lines running in the wheel wells to the front wheel hub.

The rubber rots and falls off and causes an air leak. Very inexpensive to replace with new hose.

The compressor should not run when key is off.

You still might have GPs that need replacing but you can test w/out pulling valve covers. Look at KLHansons post above. In the signature is a link for COLD START NO START.

Also look at your receipt, the AIH relay should be a different P/N that your GPR. I removed my AIH.
 
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