Ran into a real strange problem while out cruising on the GMC's 1st night cruise last Sat night. All the lights worked when static tested so I didn't think anything about trying it out at night.
When dusk hit I turned the lights on and carried on. After a short while I started noticing the ammeter jumping around from charging to "0" then I notice the gas gauge, an aftermarket Autometer gauge, started showing erratically, from 1/2 full to 1/4 full and back again. The gas gauge has been very steady before this time The voltmeter was showing 14 1/2 volt charging which is a volt higher than normal and while all this was going on the electric fan stayed on, even when temps were under it's shutoff (approx 185 degrees). It got me home and I didn't work on it until yesterday. /
Heres what I found, a wiring issue with the old cloth covered right side head light wiring, a loose toggle switch which is my bad, a blown Hi beam indicator lamp (maybe the original 6 volt, I couldn't tell) and a massive current draw that would come and go due to vibration and bouncing around.
The right side headlight worked on Hi beam but not on low beam. The low beam 20amp glass fuse was blown which killed lo beam on both headlights. The Hi beam indicator was blown. So I made it home running Hi beams and didn't know it.
The truck is a mixture of old and new wiring. The headlight wiring is old cloth covered and was wrapped in elec tape by persons unknown for how long unknown.... What happened is the low beam wires insulation frayed as did the ground wires and the vibration caused them to short together which blew the fuse. Had to cut away alot of tape to find it. The elec fan circuit I ran with new wiring uses a ground to throw the fan relay. I re-purposed a toggle switch and it's 2 wires someone had installed on the dash for purposes still unknown to me and I used it as a fail/safe toggle switch to throw the fan relay in the event of a sender failure.
The switch wasn't as tight as it should have been and the bottom terminal started making contact to the metal dash due to the looseness and vibration. I corrected this most-scosh.....
Replacing that blown HI beam indicator lamp was probably the most trouble. Due to the firewall mounted power master cylinder and the bracket under the dash, there was barely enough room to reach the backside of the gauge while pushing the lamp socket back in.
So it looks like 3 separate electrical problems hit at about the same time.
I'm really glad I kept the ammeter wired in the truck. Although the voltmeter is a better indicator of the charging systems performance, the ammeter is a good indicator of the entire trucks electrical performance.
Went on a nice 2 hr cruise today and all is well, for now anyways LOL.
