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Old 12-31-2018, 05:41 PM   #1
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Join Date: Oct 2005
Location: North Idaho
Posts: 275
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.
1980 K10 Suburban Silverado, original 350 w/Qjet swapped to 406sb, TH350C swapped to TH400/205
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