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Old 12-31-2018, 05:41 PM   #1
SilverMiner
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Unfused battery drain

Folks - here's my problem: 1980 K10 Suburban with original wiring. The only molestation is my addition of a separate auxiliary circuit through a fusebox which I added and have already eliminated as the source of the drain.

The multimeter says there is a 0.69 amp draw with the key off. This is apparently enough draw to repeatedly kill my 2 year old battery overnight. Emptying the fuse block does nothing to impact the parasitic drain. Removing the BAT wire (circuit 2C) from the alternator also does not help.

If I disconnect the wires connected to the junction block on the firewall above the drivers side head, the amp draw finally goes to zero. Careful examination of the 1980 wiring diagram suggests circuit 2E is the source of all my troubles. It seems to power the headlight switch, the interior lights, and ????. I'm a trained engineer so it's difficult for me to admit difficulty reading a wiring diagram, but there it is.

Can anyone suggest further diagnostic steps? The headlight switch was replaced with an NAPA unit some years ago, but could it still be a source of the problem? Or could it be an issue with the door switches that control the interior lights - but removing the "courtesy lamp" fuse does not impact the amp draw.

I am stumped, so any help would be greatly appreciated.
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1980 K10 Suburban Silverado, original 350 w/Qjet swapped to 406sb, TH350C swapped to TH400/205
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Old 01-01-2019, 12:44 AM   #2
dmjlambert
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Re: Unfused battery drain

What does it do to your current draw if you disconnect the 2-wire plug from the alternator?
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Old 01-01-2019, 06:44 AM   #3
Wgesnerjr
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Re: Unfused battery drain

unplug the headlight switch to rule it out as the culprit. Also try pushing the door pin switch in while testing. This circuit may also run the cigarette lighter. make sure it's not pushed in slightly.

One time on my brother-in-law`s 72 Monte Carlo, he has a similar problem. drove me crazy for a week. Turned out it was the memory circuit inside the aftermarket stereo. For some reason it was drawing way more and would kill the battery in a few days if not started daily. Temporarily ran the memory wire to a switched 12v and battery was good from then on out. Down side was he lost the time and station each key cycle. A year later he replaced the head unit an all is fine.
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Old 01-03-2019, 01:00 PM   #4
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Re: Unfused battery drain

I removed the 2-wire plug to the alternator, but no change.

The headlight switch defeated me last night because I had forgot about the hassle of removing the AC duct below the dash to access the knob removal button. I'll try again tomorrow.
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Old 01-08-2019, 01:21 PM   #5
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Re: Unfused battery drain

An update to close this thread -

The headlight switch was not the source of the drain. Also as a note to others who may read this in the future, I was wrong to think the AC duct below the steering wheel required removal. Simply unscrewing and moving the lower left dash vent allowed access to the headlight knob button.

I now believe the drain is due to the door switches for the interior lights although I can't prove it conclusively. The switches appear to be in poor condition or I'd test to see if removing them solves the problem. The measured drain changes slightly as I repeatedly open and close the doors. I was able to get the drain dropped to below 0.50 amps (how? don't know - magic maybe), which shouldn't be enough to kill a good battery just overnight. I'm running a Hellroaring dual battery setup that allows me to "self jump" so until the weather improves and new switches arrive I may just live with the situation.
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Old Yesterday, 11:13 AM   #6
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Re: Unfused battery drain

Final update - problem solved!

The courtesy lamp door switches were replaced, connections cleaned and wires inspected. No change to the 0.50 amp drain. Great frustration.

So, back to basics. I once again went through the process of individually removing connections to try to isolate which circuit the draw was on. In the course of completing that tedious step, I saw a splice that I had failed to notice earlier.

Back in 1980 according to the paper work in the glove box, my Suburban had a hydraulic Kelsey-Hayes trailer brake installed at the dealer. Rather than running a proper wire with connector to the junction block on the firewall, the installer did a ScotchLok into the always hot wire. Very disappointing - as I remember it, ScotchLok's were hated by competent technicians even back then. I repaired the ScotchLok scar with a new butt connector and heat shrink.

Removing the power to the brake controller has eliminated the unfused drain, which makes me very happy. I don't know if the drain indicates a fault with the old Kelsey-Hayes - it has always worked great, so I'll just have to remember to re-connect things in May before camping season begins.
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