71 GMC lights and blinker problem need help

[mttnlsn]

I am working on a 71 gmc 3/4 ton 2x4. My problem is when the head lights are OFF my blinkers work correctly. When my blinkers are off my head lights work correctly. When my headlights are on and I try my blinkers my dash board lights blink, the blinker arrows are lit up. When I switch from hi to low beam half my dash board lights go out all together? If I turn my light dimmers down all the way the blinkers work better, but not perfect. I have installed a new light switch and blinker wiring harness in the column. Any ideas?? This is killing me. I hate electrical problems. Thanks for the help. This is my first post.

[PanelDeland]

Welcome!!! I'll tell you the same 2 things everyone else will.Check your grounds.Most electrial problems with these trucks are due to bad grounds and it sounds like that is what you have.Also check your connections at all connectors and for bad splices.40 year old trucks tend to have been messed with a bit and adding trailer lights,fog or driving lights and such was common.Anywhere these have been spliced in may cause a problem.

[mttnlsn]

thx for the help i will check it all again. the lite swich grounds to the dash, do you know where does the blinker swich ground? or the color of the ground wire for the blinker swich?

[Stocker]

Welcome to the boards from N. Calif!

Sounds like a can-o-worms, and possibly more than one problem.

When the turn signals don't work, but the green arrow lights up in the dash, the problem might be bad grounding of the front side marker lamps. Happens more often in damp weather. They ground through their mounting screws.

[mttnlsn]

thanks for the help on that. i will go out and have a look at the lights on that. my son installed them so i will double check. i hate electrical problems.

[Classic Heartbeat]

Sounds like to me something is wired wrong. Who wired the turnsignal switch? Nobody that I know of sell just the turnsignal switch wire harness. Could also have a bad dimmer switch. (doubtfull but could) Grounding is always an issue if not done correctly, but the problems that you discribe are more than that. Sounds like you are getting power feeding back through the harness somehow. This is why I asked about the turn signal switch harness. WES

[mttnlsn]

bought new turnsignal switch harness from Classic Parts of America product code 53-510 and installed it. When i unhitch the harness from the pickup the head lights and dash lights and dimmer work properly. when i rehook up the turnsignal harness to the truck and leave the lights off the blinkers work properly. when i turn on the lights and try the blinkers they work but not with the same spark as when the lights are off. when the lights are on and i use the turnsignal lights on the dash are on. they will kinda blink if i turn on them on. bad deal is the problems are not always the same. Yes i agree i am getting back feeding to the dash or to the new turn switch. i have checked all the grounds i can find. cleaned them and replaced with no help. i am going to order a wireing diagram for the truck from Classic parts $4.95 and study it for a while. thanks for the hlep any ideas are always helpfull.

[northerngmc]

I had the same problem last fall. When I turned the headlights on the turn signals would not work.

I found out that the ground wire from the bottom of the cab to the frame was broken. Fixed that and the problem disappeared.

Check your ground wires or simply install a wire from the cab to the frame.

[cdowns]

in order to work properly each and every light bulb needs to b grounded