1988/1993 silverado c1500 electrical gremlins

[broughy84]

Okay, so I have my 88 silverado. I recently put in a drivetrain/wiring harness/ECM out of a 1993 c1500. All was well for a while. Until Sunday. We were at the stations cleaning the fire engines for the parade, it was about 1 am and I was ready to go home. When I started the truck, it sounded a bit funny, but didn't think to much about it until the moment I turned on the headlights and they were EXTREMELY DIM. My first thought was the alternator. The gauge inside reads below 9 with the lights on and 14 with the lights off. Even the slightest bit of draw causes the volt gauge to drop like a rock. I got out and figited with the battery cable. When I pushed on it, the lights came up, the truck ran good, when I let off, no dice. So I cut the end off and put a new end on. Didn't work. Did the same thing. So I swapped batteries incase this one had a bad post in it. No luck. So I changed the battery cable, no luck, so I changed the main wire running to the junction block on the fire wall, no luck. So I changed the alternator. NO LUCK. The entire time, I checked everything with a volt meter. I have .2 ohms resistance in each battery cable, so my cables are good, I have 0 resistance from the frame to the negative post so I have a good ground. The voltage with the truck running at the battery is 14.8, at the alternator 14.8. This is with the lights on or off. I have checked all fusible links, they have the same on both sides , 14.8. Now, here's the puzzler, If i check voltage at the juntion where the harness meets the firewall, it is 14.8, if I check it on the back side on the fuse box i get 8.5V +/- 0.2.

My next step is to change all fuses, wire around all the fusible links to see if there is infact a voltage drop across one, and pull the dash to check my wiring harness.


It's funny though, because it isn't the factory stuff that it is limited to. My emergency lights, which come off the junction block are down to 8.5 +/- 0.2 also.

Any suggestions???

[MT-2500]

Bad wire or connection.
Start a battery and check the power fed all of the way to where it is losing voltage.
You Might run a jumper wire around the fire wall wiring plug in.
I have had some bad plugins there.
Good Luck

[broughy84]

After pulling my hair out, and the dash to check all wiring. I ruled out the power side of the equation. So I started looking at grounds. I feel like an idiot too. I checked all engine grounds, all frame grounds, but I didn't check the ground from the battery to the fender. When I loosened it and wiggled it it fell apart in my hand. Put it back together and tada, magically everything works again.

[MT-2500]

Thanks for posting back how it went and the fix.
Yes bad grounds will do things like that.
Bad ground can make everything do strange things.
Glad you found it.