Strange turn signal issue on 72 C-10

[72bowtiestepper]

Wrapping up the multi-year restoration build on my 72 stepside and have run into a problem with the turn signals. With headlights OFF, all signals front & rear including front marker lights & dash indicators work great.

With headlights ON all signals are REVERSED....Switch lever down for a left turn..the right signals front & rear are activated. Switch lever up for a right turn....the left signals front & rear are activated. The dash indicators are opposite also. The brake lights are fine and work with headlights off or on.

I searched in old forums about issues with turn signals & found many people have had grounding issues, so I ran a dedicated ground to each signal housing front & rear.....No change. With headlights on signals are still reversed left to right & right to left. Any ideas what could be causing this ??

[pjmoreland]

Wow. That is a strange one. When I run into mysterious problems like this, I like to eliminate big sections of the system until I get down to something that works, and then I start adding small sections back until I re-encounter the issue. If you unplug the tail light harness under the dash where it goes through the firewall, do your front turn signals work properly with the headlights on?

[72bowtiestepper]

Originally Posted by pjmoreland

Wow. That is a strange one. When I run into mysterious problems like this, I like to eliminate big sections of the system until I get down to something that works, and then I start adding small sections back until I re-encounter the issue. If you unplug the tail light harness under the dash where it goes through the firewall, do your front turn signals work properly with the headlights on?

Thanks for your suggestion....will try that tonight when I get home.

[Dr Jekyll]

It sounds like a ground issue. Are your fenders, cab, core support and bed grounded to the frame? Check ALL grounds.

[72bowtiestepper]

Originally Posted by Dr Jekyll

It sounds like a ground issue. Are your fenders, cab, core support and bed grounded to the frame? Check ALL grounds.

That's what I originally thought Dr. Jekyll....All grounds check out good & as I said, I even ran extra ground wires to the front & rear parking light housings & tail light housings.

[Dr Jekyll]

It’s hard to diagnose over the internet, but I would double check my negative battery terminal ground to the frame and all the way to the body panels where my ground wires are attached. You should have grounding straps attached to the frame on any panel that your grounding to, don’t rely on panel fasteners to supply the ground. Use a voltage tester or light on attachment points. since the issue shows up when you turn the headlights on, headlight wires need to be chased as well, in fact that’s your primary suspect.

I’m not sure, are headlights grounded at the corre support or at the fuse box?

Edit: headlights ground at the core support. Is your headlight switch grounded? If so how is the cab grounded?

[72bowtiestepper]

[QUOTE=Dr Jekyll;8843822]It’s hard to diagnose over the internet, but I would double check my negative battery terminal ground to the frame and all the way to the body panels where my ground wires are attached. You should have grounding straps attached to the frame on any panel that your grounding to, don’t rely on panel fasteners to supply the ground. Use a voltage tester or light on attachment points. since the issue shows up when you turn the headlights on, headlight wires need to be chased as well, in fact that’s your primary suspect.

I’m not sure, are headlights grounded at the corre support or at the fuse box?

Edit: headlights ground at the core support. Is your headlight switch grounded? If so how is the cab grounded?

Attachment 2064442
Thanks for attaching the diagrams. My headlights are grounded at the rad. support....will have to check if the headlight switch has a good ground. Your help is apprieciated !

[Andy4639]

I just had this same problem. Look at this thread. This is what I found.


http://67-72chevytrucks.com/vboard/s...d.php?t=814092

[Bronik290]

I had a problem with my 67 that blew the cluster and tail light fuse along with the dome light and it ended up being a bad headlight switch. First happened with the headlights on and then would happen with the headlights off. New Headlight switch fixed the problem.

[custom10nut]

It’s all about the grounds.

[72bowtiestepper]

I assume the headlight switch gets ground from the dash panel...correct ? I will run another ground wire direct from the neg. battery term. to the dash tonight & see if that makes a difference. If not ...will order a new Headlight switch.

Andy...I have not blown any fuses at all...just have the prob. with the turn signals being reversed side to side...only when Headlights are on.

Thanks to all for your help....I am confident I will get to the bottom of this...If not...will only drive the truck in the daytime w/ no headlights LOL !

[Dr Jekyll]

Headlight switch is grounded to the dash using the grounding terminal on top of the switch. You can’t see it looking up at switch while it’s installed and your looking from the floor. Best way to install if it’s missing is: remove the switch, install pigtail/jumper, reinstall switch, connect terminal lug to dash.

[72bowtiestepper]

Originally Posted by Dr Jekyll

Headlight switch is grounded to the dash using the grounding terminal on top of the switch. You can’t see it looking up at switch while it’s installed and your looking from the floor. Best way to install if it’s missing is: remove the switch, install pigtail/jumper, reinstall switch, connect terminal lug to dash.

Attachment 2064641

Thanks Dr.Jekyll....will definitly check it out tonight.

[72bowtiestepper]

Originally Posted by Dr Jekyll

Headlight switch is grounded to the dash using the grounding terminal on top of the switch. You can’t see it looking up at switch while it’s installed and your looking from the floor. Best way to install if it’s missing is: remove the switch, install pigtail/jumper, reinstall switch, connect terminal lug to dash.

Attachment 2064641

OK....making some progress ! Removed HL switch & soldered a ground wire from the grounding terminal to a good ground on the dash panel.
Left front & rear as well as Right front & rear are functioning proper now with Headlights OFF & ON.
Indicators on dash are STILL REVERSED however (Left indicator flashes when Right signals are on.....Right indicator flashes when Left signals are on.) ?????

[Dr Jekyll]

Is it possible that your wires got swapped in your turn signal switch connector? If all your grounds are good, the easy fix would be to swap them in the half moon connector on the steering column. Here is a forum thread that covers this topic
http://67-72chevytrucks.com/vboard/s...d.php?t=712235

[conoco]

I know it sounds stupid but I had the same issue with my k2500. I spent a week of my life following electrical lines, pulling my dash apart, cleaning and replacing all the grounds, replacing headlight switch and also my foot high beam switch. So much stuff I checked and replaced.

My problem ended up being the bulb that was used for my front turn signal and running light was loose. I replaced the bulb and everything work correctly now. Inwas so pissed. I should have checked all the bulbs first. Instead I got to know my truck a little better lol. Lots of good resources on the forum. Good luck.

[72bowtiestepper]

Thanks again Dr.Jekkle...You have been a great help to me with this problem & also thanks to VetteVet with that guide to checking the turn signal switch.

Will be checking it this weekend !

[72bowtiestepper]

Originally Posted by conoco

I know it sounds stupid but I had the same issue with my k2500. I spent a week of my life following electrical lines, pulling my dash apart, cleaning and replacing all the grounds, replacing headlight switch and also my foot high beam switch. So much stuff I checked and replaced.

My problem ended up being the bulb that was used for my front turn signal and running light was loose. I replaced the bulb and everything work correctly now. Inwas so pissed. I should have checked all the bulbs first. Instead I got to know my truck a little better lol. Lots of good resources on the forum. Good luck.

I know the feeling ! Spent way too much time on this problem, but it was a learning experience for sure.

[Rick Bollinger]

There is a small screw that goes through the printed circuit on the back of your gauge cluster. This is the primary ground for all your dash lights including your turn signal lights. This screw contacts your ground loop in your printed circuit and the back of your instrument panel. If this is not making a good ground at this screw it will do what you describe. Yes just a small 1/4" screw can do all of this. It allows power to back feed through your harness and cause kaos

[72bowtiestepper]

Originally Posted by Rick Bollinger

There is a small screw that goes through the printed circuit on the back of your gauge cluster. This is the primary ground for all your dash lights including your turn signal lights. This screw contacts your ground loop in your printed circuit and the back of your instrument panel. If this is not making a good ground at this screw it will do what you describe. Yes just a small 1/4" screw can do all of this. It allows power to back feed through your harness and cause kaos

Thanks for that info. Rick !
Will check that out when I have the cluster out...I am replacing the fuel gauge before putting the truck on the road.

[Rick Bollinger]

you can check it while it is installed with a 1/4" socket and ratchet. But don't over tighten it that will twist your printed circuit. Loosen it up first then re snug.

[Andy4639]

Originally Posted by Rick Bollinger

There is a small screw that goes through the printed circuit on the back of your gauge cluster. This is the primary ground for all your dash lights including your turn signal lights. This screw contacts your ground loop in your printed circuit and the back of your instrument panel. If this is not making a good ground at this screw it will do what you describe. Yes just a small 1/4" screw can do all of this. It allows power to back feed through your harness and cause kaos

My post back at #8 talks about all this but I guess he didn't read it. I tried to help. I had the exact same problem he is having. The post starts out with another problem but if you read all of it it ends up explaining it.