Electrical head scratcher

Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
5,630
1,037
113
Queens, NY
#1
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????
 
Last edited:
pagrunt

pagrunt

Comic Book Super Hero
Sep 14, 2014
2,762
1,475
113
Shelocta, Pa
#2
First thing comes to mind would be the dash common grounds, second would be something chewed some wires & making contact.
 
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
5,630
1,037
113
Queens, NY
#3
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

pagrunt

Comic Book Super Hero
Sep 14, 2014
2,762
1,475
113
Shelocta, Pa
#4
Possible something was rewired to make the removed cluster to work?
 
Ribbedroof

Ribbedroof

Royal Smart Person
Jan 4, 2009
2,276
816
113
Wellston, OK
#5
Engine to chassis ground? Body to engine ground?
 
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
5,630
1,037
113
Queens, NY
#6
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

ssn696

Comic Book Super Hero
Supporting Member
Jul 19, 2009
3,165
1,089
113
New Mexico
#7
Name her Christine.
 
1evilregal

1evilregal

Royal Smart Person
Apr 23, 2009
2,235
1,113
113
Greensboro, NC
#9
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

airboatgreg

Royal Smart Person
Oct 2, 2016
1,167
732
113
#10
No doubt a bad ground. Make sure a block to bulkhead ground and the wiper motor has a squirrelly ground strap set up.
 

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