I thought I'd write this up for entertainment/educational purposes......
My '53 gmc pickup is mounted on a '76 gmc chassis. When I got it about a year ago it had a battery drain that would make it fail to start after a few days of sitting. The starter always sounded extra loud and the taillights would go out when the headlights would go on. I have finally had a chance to work on it during my vacation this summer after completing a big pier biulding job for my friend.
I "painted" it recently and am now moving on to the mechanicals. I know, backward, right? Anyway, I attempted to dissect the spaghetti wiring harness under the dash in an attempt to locate the problem. In the process, I discovered the taillights went out when the headlights came on. Getting the light switch out was a booger and had I not looked it up on the internet I'd never have known about the button on the switch body that releases the knob pull shaft! A fellow stovebolter told me about the switch position that controlled his parking lights which turned them off when he turned on the headlights. Got 'em fixed by moving the taillight wire to the right terminal (THANKS!). Well, not long into my short-locating adventure, I burned out the fuse in my cheapo meter, so I could only see voltage and resistance. I kept seeing 12.4 volts between my negative battery post and ground strap no matter what I did which was driving me bonkers. I pulled every fuse and disconnected every wire to no avail. This has gone on for about 3 days and about 15 or more hours a day. I finally resorted today to cutting all the main wires. Still, I had 12 volts from neg. post to ground if the main power wire from the battery to the starter and the wires from there to the alternator were attached. I replaced the alternator since I burned out the diodes probably due to cranking the motor with a 1/4 charged battery. Still no go. I replaced the starter and solenoid. Still no go. I finally decided to replace the fuse in my meter so I could find out just how many amps were leaving the battery with only the starter and alternator wired. It was only about 1 millivolt. No big deal, but at this moment, I still don't know why theres ANY power or voltage leaving the battery with nothing on. I connected the main power wire that feeds the cab and suddenly got about an 85 milliamp current leaving the battery so I knew I had a short inside the cab now. I started pulling wires and fuses again..... On a suggestion from someone answering someone else's question on battery-drain troubleshooting I hooked up a cheapo test light between the neg. battery post and ground strap. It faintly glowed. When I pulled the tach. power wire it went out. SO...I've found my short. After hooking everything else up I had cut off, I now only have about a .4 to a .8 milliamp power loss from the battery. I think I can live with that. Now to find the short in the tach power wire and finish the job by reinstalling my radio, carpet, seat, etc. BTW, the new starter sounds nice now and the new alternator should give some semblance of safety as to that aspect now.
I hope my story might help someone else avoid my misadventure in wiring and perhaps give some of you real mechanics a little chuckle at my idiocy. Thanks for your help, also!
Later,
Jason
