Author Topic: Electrical Drain on '78 C20  (Read 3734 times)

Offline alhrensblade

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Electrical Drain on '78 C20
« on: May 17, 2006, 02:13:00 AM »
Hi all,

I'm trying to track down a slow electrical drain somewhere in my truck. I've already checked the fuseblock, but wasn't able to find the problem- and I shattered most of the fuses (they were probably originals, heh) pulling them, so am a touch reluctant to try that method again. Would anyone be so kind as to furnish me with a list of the systems that are /supposed/ to have always-on connectivity? I know it's not the memory wire for my stereo- that's been disconnected for who knows how long, until tonight. But even with the truck off, and everything shut off, disconnecting and reconnecting the positive battery cable causes a rather impressive spark.

I'm going to be replacing the alternator- and starter-ends of the cables tonight or tomorrow (they're a bit frayed). One thought that I did have is the small connector on the back of the alternator (an eyelet with a red wire attached, which is held onto a small post with a nut). What purpose does that serve, and why are there two posts?

The drain is slow enough that as long as I drive it to work every few days, it doesn't die completely, but if I leave it for more than a week or so, the battery's toast. The battery itself has been tested repeatedly and thoroughly, and holds a charge in and of itself quite well.

Edited by: alhrensblade at: 5/17/06 1:15 am

Offline Lt.Del

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> Electrical Drain on '78 C20
« Reply #1 on: May 17, 2006, 08:53:00 AM »
Try reading this.  It is a previous post of a similar issue....  Wait, this is your post from a couple of months ago.  

As for the alt.  The red wire attached to the post is the charging wire.  By putting on a volt meter it should read about 14 volts when running.

I wouldn't change your alt unless you are sure it is that.  Unhook the wire of the alt.  Let the truck stand for a day or so and see if the battery volts drop w/out the alt hook up.  Same goes for your starter, unhook those wires and let truck sit.  Check battery volts after all that.

unless you have some aftermarket wiring done on your truck, all circuits should pass thru your fusebox.  As mentioned on an earlier post, take each fuse out, one circuit at a time until you no long have a drain to find the faulty circuit.

IF nothing is "on", it may be your ignition switch worn.  Does your fan blower on the firewall stay on for heat/ac?


Edited by: SgtDel at: 5/17/06 11:18 am

Offline 82Silvrdo454

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Re: Electrical Drain on '78 C20
« Reply #2 on: May 17, 2006, 06:42:00 PM »
I had a short one time drawing power from my battery.  The way I found it was, I took a fuse out and pulled the positive lead off the battery looking for a spark when I touched the lead to the positive post, and went through every fuse being sure to replace the fuse that I had pulled before pulling a new one.  Turned out to be diodes in my alternator, changed the alternator and problem fixed.  Don't worry about the spark, just don't wear any jewelry, ect. rings, braclets.  

Offline alhrensblade

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Re: Electrical Drain on '78 C20
« Reply #3 on: May 17, 2006, 09:55:00 PM »
Thanks much for the thoughts... I don't know about the actual 'switch' for the ignition, but the key cylinder is new as of last year, same for the alternator (it was in bad shape, and would periodically stop charging altogether). I'll try checking the fuses again when I get the chance. I don't /think/ I have any aftermarket wiring done- this was obviously a work truck for all of its life (in fact the person who owned it before me used it pretty much just to haul stuff to the dump). I can check, though- the only wiring I've done is a stereo memory line, and that was recent and runs to the terminal next to the dome light on the fuseblock.

Online VileZambonie

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Re: Electrical Drain on '78 C20
« Reply #4 on: May 18, 2006, 12:30:00 AM »
OK So if the battery passed the load test and the charging system is ok you have a parasitic draw. Disconnect the negative battery cable and hook a digital multi meter up in series between the battery terminal and the battery cable. On the milliamp scale you should have no more than a 32ma draw. If you don't have a DVOM hook up a test light in series the same way and let us know if the light is on, and pay attention to it's brilliance. Make sure the ignition is off, and all accessories when doing this test.

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