Turn Signal Issue

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Aug 12, 2021 | 05:07 PM

TXBuilder

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Joined: May 2020

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Turn Signal Issue

I have a 1976 F150 4wd . The front left turn signal will not work, all the others do. When I turn on the lights, all the turn signals stop working. I have checked/replaced all bulbs, cleaned all bulb sockets, and inspected wiring. I can find no issue with the wiring. Any ideas?

Thanks

Aug 12, 2021 | 09:48 PM

Idaho Highboy

Tuned

Joined: Jan 2017

Posts: 338

Likes: 8

From: North Idaho

TX, do you have a test lamp that you can pierce the wire ahead of the front left socket to see if a signal is making it that far? Can you be more specific re: any troubleshooting you've done?
- IH

Aug 12, 2021 | 10:46 PM

John89

Fleet Mechanic

Joined: Jul 2017

Posts: 1,448

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From: East Texas

Check and clean all grounds, even the ones not specifically associated with the lights.

Battery to block
block to frame
engine to firewall
etc...

Then check all sockets with test light/ meter as mentioned.

I think everyone on here has chased lighting gremlins at least once.

Aug 13, 2021 | 06:52 AM

TXBuilder

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Quote:

Originally Posted by Idaho Highboy

TX, do you have a test lamp that you can pierce the wire ahead of the front left socket to see if a signal is making it that far? Can you be more specific re: any troubleshooting you've done?
- IH

I have not used a test lamp. I have inspected and cleaned all light sockets, checked and replaced all bulbs and inspected the wiring for ant visible damage. Last night i replaced the flasher module and the blinkers all started flashing when the right one was turned on, none when the left was turned on. I reinstalled the old flasher module and now the same thing, when you turn on the right side they all come on, engage the left and nothing works. I will say the left front appears to be much dimmer when they all come on.

Aug 13, 2021 | 04:33 PM

Idaho Highboy

Tuned

Joined: Jan 2017

Posts: 338

Likes: 8

From: North Idaho

Could be a couple of things if one side isn't working and we shouldn't assume that whatever is affecting the forward signal is affecting the rear. Can you use your multimeter lead to poke through the wiring ahead of your front and rear left sockets to see if you get 12vDC when you activate the turn signal?
- IH

Aug 14, 2021 | 10:30 AM

5851a

Logistics Pro

Joined: Oct 2006

Posts: 4,029

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From: East Central Ia

99% of the time it will be bad ground. The Ford turn signal sockets have 2 piece construction on the ground contact wire. It can and will corrode at the hidden joint, you can have a good ground wire going in but no ground on the bulb side. The replacement sockets don't match the factory colors so you have to check them out.