Electrical head scratcher

[Bonnewagon]

1980 Pontiac, full gauges and tach, electric choke, delay wipers, power windows, no AC, no radio, wiring "looks" intact. But when you turn on the running lights, the dash turn signal indicators glow, the tach jumps 1000 rpm, and the gauges sway. If you turn the dash lights dimmer off, it doesn't happen. I know what you're thinking-BUT. Turn on the wipers and the same thing happens and if you push the washer it gets way worse. Then wipers only work if you futz with the switch, and if they feel like it, they work great, sometimes. But if you don't use any lights or the wipers, all gauges, tach, directionals, stop lights, emergency flashers, everything works. All the external lights work but then that causes the issue. The grounds look good and I can't find any smooshed or pinched harnesses. All fuses were wrong values, missing, or blown. I set them straight. Short of changing the entire harness- what could this be????

 

[pagrunt]

First thing comes to mind would be the dash common grounds, second would be something chewed some wires & making contact.

 

[Bonnewagon]

I had the gauge cluster out because it was the wrong one. Before I put the right one in I gave a quick check of the wiring and all looked pretty good. Nothing ripped or broken, grounds were intact, even had the plastic tubing on the harnesses.

 

[pagrunt]

Possible something was rewired to make the removed cluster to work?

 

[Ribbedroof]

Engine to chassis ground? Body to engine ground?

 

[Bonnewagon]

I was just under there today. The main body/engine ground cable was left off so I re-attached it. No change. The cluster was DOA so I removed it and noticed the wire harness did not match the printed circuit. I'm not even sure what year it was from but the one I put in was correct and all the wire colors were compatible. The cluster works great now except for the craziness when you use the lights or wipers.

 

[ssn696]

Name her Christine.

 

[fleming442]

Just saw something like this on Clutch's squire body: one of the ribbon pins on the PCB folded over- it was the ground for the cluster.

 

[1evilregal]

long shot, but maybe something in the steering column? when you said the wipers sometimes work, column switch came to mind, along with dimmer switch/turn switch...

 

[airboatgreg]

No doubt a bad ground. Make sure a block to bulkhead ground and the wiper motor has a squirrelly ground strap set up.