Parisitic Drain - 1980 Suburban

[SilverMiner]

I spent most of this evening attempting to hunt down a parasitic drain in my 1980 K10 Suburban.

I disconnected the negative cable and measured full battery voltage between the cable and the terminal using a digital multimeter even with the key off. I then proceeded to individually disconnect every item from the fuse block one at a time (more than once, actually, because I started out forgetting to close the door and of course the dome light was active). Unfortunately, removing fuses and connectors made no difference.

I wasn't able to get an accurate measure of how many amps the drain was pulling. My multimeter maxes out at 150 milli-amps, and whatever circuit was open is drawing more than that.

Should I be checking somewhere else beyond the fuse panel? I am already beginning to suspect the starter and/or solenoid and may replace them tomorrow just because everything else on the rig has been original so after nearly 34 years I should do it just on general principal.

Thanks for the help

[Warrens69GMC]

Have the alternator for an open diode. It will charge like normal, but will drain your battery when off.

[SilverMiner]

The drain persists even with the existing alternator fully disconnected.
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[andrewmp6]

Another way is to think about what don't work that should or works when it wants.

[hrc200x]

Just went through this same thing in my '02 super duty diesel. It ended up being the aftermarket edge evolution chip, I to figured alt so unplugged that and it stayed the same. Some tips I found out when researching, look truck over when its completely dark, no flashlights, no moon out, etc...is anything on or glowing? Find a perfectly quiet area and with everything off can you hear any humming, buzzing or anything running? friend of mine with a '99 chevy 1/2 ton found a stuck power seat switch on when everything was quiet, with the switch on it would give seat motor power for a few seconds then I suppose time out and quit for awhile, then give it power again.

Does your meter have a 10 amp reading? You may have to move one of the probes on the meter its self to a different hole.

I'm not sure but does the distributor get power even when the key is off? If it does maybe try unhooking the wire that plugs into it.

How many days can it sit before battery goes dead?

This probably won't pertain to your vehicle but incase you run accross a newer vehicle with the same problem. My ford has two batteries. To do the drain test I was told to unhook both and just run the meter between one battery with the other unhooked, when I did this there is so much electrical stuff on newer vehicles that take a lot of power to "boot" up when the battery leads are hooked up that it would max the meter out and I think blow a fuse in the meter. I had to hook up the other battery to the bat cables then hook the meter to the other batteries cables. Then disconnect the bat thats got the cables to it, making it so the computer never lost power. Also found out that as soon as the computer lost power these things that "boot" up can stay on for 25 minutes and I've heard even longer in different vehicles. I don't know how a person could test this on a vehicle that has lots of boot up amps with only one battery, only thought would be to disconnect the neg cable and run a wire between it, let the vehicle unboot and while the wire was still hook up also hook up the meter then disconnect the wire.

[SilverMiner]

I will try some of those suggestions. I'd never considered the HEI distributor as a possibility but it is easy enough to disconnect and test. I can probably bypass the solenoid as well and see what happens.

The rig also has A/C and power locks but no rear air or power windows. They should have been dealt with when I was pulling fuses.

Last night I was much more confident thinking the 1980 would be easier to troubleshoot than my 2004 Tahoe with its sleeping/waking systems.
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[mrolds88]

I would disconnect the wiring at the firewall. This way you can compartmentalize where the problem is.Then check your readings. Had a similar issue with a 70 442 years ago. Turned out that the A/C cutout switch on the back of the head wasn't plugged into the right wire.

[SilverMiner]

SUCCESS!!!

Thanks to your suggestions, I was able to isolate the problem. I had searched the board before asking this question, and despite it coming up more than once for many different age vehicles, I didn't see a thread where a final conclusion had been determined. So I won't make that same mistake...

hrc200x - your suggestion about checking for a "10 Amp" position was spot on. I would have been way ahead of the game if I actually understood my multimeter, but of course the instructions disappeared a decade or more ago, but your clue saved the day. I was able figure out how to properly measure the amps being pulled by the mysterious circuit, which turned out to be 0.41. With the dome lights on (80 Suburbans have two) the total draw was ~1.3 amps. Knowing that the dome lights accounted for ~0.9 allowed me to ignore the whole "leaving the drivers side door open" issue and move much quicker.

mrOlds88 - your suggestion to isolate the firewall was also key. I tediously went through the fuse box more than once thinking it HAD to be there, but after seeing your post I checked the power post on the firewall near the brake booster. As it turned out, that was where the problem existed:

SOLUTION: (for my vehicle, anyway)

Back in 1980, the dealer installed an old Kelsey Hayes trailer brake which they tapped into constant 12V on the firewall. After I disconnected that power lead, the 0.041 amps that was draining my battery disappeared. For now, I can easily leave that off and solve my dead battery problems. In the future I intend to hunt down the reason that 0.04 amp drain exists, although I strongly suspect it is due to a 34 year old wire with bad insulation somewhere between the firewall and the trailer hitch that I will simply replace. I don't plan to hunt very hard because for the time being I can easily unplug the whole unit.

THANKS AGAIN FOR ALL THE SUGGESTIONS

[SilverMiner]

CORRECTION:

In the above post I said my parasitic drain was 0.041 amps but that was a fat finger error. In fact it was 0.41 amps.

Also, if the mods believe this thread belongs more appropriately in the Electrical Forum I'd be pleased if they moved it there.
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[hrc200x]

Thats awsome. I don't really understand the 10 amp setting on the meter, on mine anyway needing to move the probe to a different hole. In order to do that you need to break the circuit when your doing a test. Would be nice if you could turn the dial strait from 10 amps to milliamps with out having to disconnect because like I said in a earlier post some newer vehicles when battery connection is first made there is major draw that can stay on for 20 mintues or longer.

[mrolds88]

Excellent!! And ya gotta love them fat fingers!!!LOL