Left turn equals both tail lights flashing??? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

HSRACER · 07-06-2015, 01:35 PM

So I just got a new to me 69 gmc and I was inspecting the lights before driving it home. Everything works properly until I put the left turn signal on. The front flashes fine but in the rear both sides are flashing. Right turn works properly with only the right side flashing in the rear.

I pulled the connection at the rear and found both lower pronges had flashing power to them when the left turn was on, which means that the problem is up stream of the actual tail lights and rear wiring harness. The factory leads along the frame are all there and connected and the plug at the firewall is solid and correct. It then seems to go to the steering column at the lower connection point at the bottom of the column, which I thought was neutral safety switch?

Any advice of what to check next is appreciated!

70LonghornCST · 07-06-2015, 02:46 PM

You may have a short or a nick in the wire in the intermediate harness. We'll let others chime in. Maybe someone has had this same scenario with their truck.

HSRACER · 07-06-2015, 02:53 PM

Quote:

Originally Posted by 70LonghornCST

You may have a short or a nick in the wire in the intermediate harness. We'll let others chime in. Maybe someone has had this same scenario with their truck.

No I have disconnected the intermediate harness and checked it at the firewall plug and the dual signals to each taillight is there before it even goes out the firewall.

That eliminates the wiring from the firewall back. I also pulled the fuse block to see if anything was shorted in the back of it but saw nothing.

I have replaced the flasher with a couple of different ones and the problem still exists.

Could it be in the turn signal switch itself?

HSRACER · 07-06-2015, 02:55 PM

The weird thing is that the front signals work perfectly.

Mr Chevorlet · 07-06-2015, 03:35 PM

I would suspect the turn signal switch. They will do weird things! Before you take the turn signal switch out go get one and unplug the wire harness to the column and plug the new one in and see what happens.

HSRACER · 07-06-2015, 05:13 PM

Figured it out this afternoon. The turn signal switch inside the column had a metal pivot spring inside that touched the side of the column when switched to the left causing enough current to flow into the othe blinker wire that was also touching. Electrical taped the spring so it can't make contact and everything works as it should.

I thought I would share the fix. Thanks everyone for your help.

07-06-2015, 01:35 PM	#1
HSRACER Registered User Join Date: Sep 2007 Location: Katy TX Posts: 1,268	Left turn equals both tail lights flashing??? So I just got a new to me 69 gmc and I was inspecting the lights before driving it home. Everything works properly until I put the left turn signal on. The front flashes fine but in the rear both sides are flashing. Right turn works properly with only the right side flashing in the rear. I pulled the connection at the rear and found both lower pronges had flashing power to them when the left turn was on, which means that the problem is up stream of the actual tail lights and rear wiring harness. The factory leads along the frame are all there and connected and the plug at the firewall is solid and correct. It then seems to go to the steering column at the lower connection point at the bottom of the column, which I thought was neutral safety switch? Any advice of what to check next is appreciated! __________________ HSRACER Slammed 53 5 window Blown/Bagged 54 Pickup Patinaed 67 LS stepside Supercharged 67 Nova Bagged 69 Suburban Turbo'ed 5.3 LS Last edited by HSRACER; 07-06-2015 at 02:03 PM.

07-06-2015, 02:46 PM	#2
70LonghornCST Moderator Join Date: Jun 2008 Location: Modesto, CA Posts: 5,775	Re: Left turn equals both tail lights flashing??? You may have a short or a nick in the wire in the intermediate harness. We'll let others chime in. Maybe someone has had this same scenario with their truck. __________________ 2018 Chevy Crew Cab 2006 Impala SS 1965 Plymouth Sport Fury 1970 Chevy Longhorn Bucket Seats Shoulder Belts Front Tow Hooks Factory Air Factory Speedwarning, Tach & Vaccum Factory Tilt CST Package AM/FM Radio Bumper Guards Richard 70 Longhorn CST Build Adding an AM/FM Decal Last edited by 70LonghornCST; 07-06-2015 at 02:46 PM. Reason: add info

07-06-2015, 02:55 PM	#4
HSRACER Registered User Join Date: Sep 2007 Location: Katy TX Posts: 1,268	Re: Left turn equals both tail lights flashing??? The weird thing is that the front signals work perfectly. __________________ HSRACER Slammed 53 5 window Blown/Bagged 54 Pickup Patinaed 67 LS stepside Supercharged 67 Nova Bagged 69 Suburban Turbo'ed 5.3 LS

07-06-2015, 03:35 PM	#5
Mr Chevorlet Rusty Nuts Join Date: Sep 2008 Location: Clever Missouri Posts: 1,338	Re: Left turn equals both tail lights flashing??? I would suspect the turn signal switch. They will do weird things! Before you take the turn signal switch out go get one and unplug the wire harness to the column and plug the new one in and see what happens. __________________ (Clever Missouri) Southwest Larry Mr Chevrolet My Build, The Marathon Truck http://67-72chevytrucks.com/vboard/s...d.php?t=604414

07-06-2015, 05:13 PM	#6
HSRACER Registered User Join Date: Sep 2007 Location: Katy TX Posts: 1,268	Re: Left turn equals both tail lights flashing??? Figured it out this afternoon. The turn signal switch inside the column had a metal pivot spring inside that touched the side of the column when switched to the left causing enough current to flow into the othe blinker wire that was also touching. Electrical taped the spring so it can't make contact and everything works as it should. I thought I would share the fix. Thanks everyone for your help. __________________ HSRACER Slammed 53 5 window Blown/Bagged 54 Pickup Patinaed 67 LS stepside Supercharged 67 Nova Bagged 69 Suburban Turbo'ed 5.3 LS



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