Hi guys, I posted a while back with a problem I'm having with my left rear turn signal/brake light. When I turn on signal, front left signal works, but not left rear, right side works fine, and also the left rear brake light won't light up, right side works fine. When I turn headlights on, the taillight on the left side lights up, as does the right side. I've checked the ground, and tried a different bulb in it. Same thing. Someone suggested the turn signal switch, however, if it was the switch, I don't think the front left signal would blink when signal is on, or the right side for that matter. Any ideas what could be the problem? Thanks in advance.

 

When a switch goes bad, it can indeed affect just one side in the back, including brakes... Granted, that's not guaranteed to be the problem, but in my limited experience it does sound like it.

I know, it doesn't really make sense, but it's the way these things are wired. One side can go out, and affect only the rear turn signal/brake (since the brake and turn signal share a wire).

 

Do you have power back to the left rear brake light? If you do and you are sure its not the switch or the ground then you have a broken wire somewhere. If someone has installed a trailer plug-in I would check there first, few people take the time to do it right and the wires corrode and lose contact or even corrode into 2 pieces..

 

If I were you (and I was in the very same position a couple weeks ago--read this thread) I wouldn't jump to change the turn signal switch.

First check the grounds at the tail light area. Visually compare it to the grounds on the other side. Then use a circuit tester to check the power to the wires and the ground...easy thing to do, just learned.

Maybe change out the socket. At least clean the connectors, but a socket is about $8 at the auto parts store.

Check to see if the wires at the connector under the dash (coming from the turn signal switch) are in place. The left rear turn signal is a yellow and black wire. Use the circuit tester.

Finally, trace the wires at the back of the truck (mine ran just under the rear bumper between the back lights, as well as up the left side of the truck above the frame....and then again out the firewall in front of driver. Check with circuit tester along the way and also check some of the plugs in between each.

If all of those things don't work, then try replacing the TSS

 

So I'm resurrecting my thread here. I re-read many of the things posted about the turn signal/brake light problems. Many said check the grounds, check the grounds, and check the grounds. Well, I'd used a wire brush and my drill on the bed of the truck where the wires for the tail light assembly, and the side marker wires attach, but I didn't clean the posts of those wires themselves. So I went out today and used a wire brush on those, and sure enough, I turned on the left signal, and boom it's working; as is the brake light when pressed. I ordered a TSS that I was going to go pick up tomorrow, so now I don't need it, saving me 72 bucks. Now my headlights aren't working, I believe it's the headlight switch, as I haven't been messing with any of the wiring for the headlights, so that leads me to believe it's the switch and not something I did to them, going to pick that up tomorrow, 15 bucks. So a word of advice, always check your grounds, no matter how well you think you did cleaning them and checking them. Thanks for all your help as usual guys.

 

Did you get a new headlight switch? Things working?

Well...I discovered something about my own turn signal and brake light issues, which I thought was fixed. It's the opposite of your problem: when my headlights are on, the rear left turn signal and brake lights don't work. Everything works with lights off. I thought I had fixed my problem

If not the grounds, not the sockets, not the TSS, could the issue be the headlight switch?

 

I had an issue once while driving at night all my lights except the headlights would go on and off. Took it to an electrical shop, they changed the headlight switch and it was fixed. Not the same situation you guys have but it might help.

 

I'm going to give it a shot, can't hurt. Local auto parts places have them or order from a place like Bronco Graveyard?

 

Headlight Switch - 18.99 @ Autozone

 

we had a shut off issue with the lights on a dent...if you hit a bump the hedlights would go off but everything else worked...so we changed the switch and that fixed that...it seems off topic but what i'm getting at is that the headlight switch can cause crazy things.

 

Thanks for asking. It's a possibility for sure, and you've replaced so many other things, what's another one to add to the list?

I did get things working, but it wasn't the headlight switch, I got a different one and put it in, and still no lights. So I fiddled with the dimmer switch, and then the lights came on, I will replace it. You might check the dimmer switch too. When you turn the headlights on, does the rear left taillight/sidemarker come on as well?

I also got a multi tester, and started at the taillights and worked my way forward checking the yellow black wire, and near the front fuel tank, I found a jumble of wires where the PO had cut into the wiring and every wire under there had 2 crimp connectors on each wire.

I cut out the crimp connector on the yellow/black, and touched the wires together, and the turn signal fired right up. But as I worked further towards the engine bay, the wiring which feeds through the transfer case mount/shock absorber, I found another problem area, over the years of movement, the coating was all worn off the wires, and a couple are completely bare.

Instead of fixing it, I'm replacing it. I went to the pull and pay place day before yesterday and scored the wiring from an extended cab that has never been cut into. Also got a dimmer switch while there, hornbar for my steering wheel, and a new heater control unit that has a factory switch in the panel for the dual fuel tanks, so I can take the toggle switch one off of my dash.

 

I had the same issue with taillights/ turn signal/ brake lights on the 76 F100. Replaced bulbs and cleaned connections inside socket, and now it works. I am having an issue with instrument panel lights, they simply WONT WORK!!!! Replaced all bulbs and the fuse. The warning lights and turn signal indicators work, but none of the other lights in instrument panel will. Any suggestions?

 

georgiaboy30755

There are basically three ways:

1) remove the headlight switch and clean the rheostat contacts and tang.

2) remove the headlight switch and take the rheostat out and clean the center contacts between the rheostat and the housing. It's easy to bend the tang that contacts the rheostat spring so be prepared to replace the switch.

3) replace the headlight switch

 

I never updated my experience on this thread (but did in another one, I think?) so...even after I got the headlight switch no go.

Turned out it was a bad socket. I had replaced it, but apparently the cheapo foreign unit I got from one of the parts stores in town wasn't good. I paid out the extra $8 for another one--I was just cycling through the fix options again--and everything worked fine. Has for over a year.

 

Dumb question. My brake lights don't work right now in my 73 but I also installed a 78/79 steering column with original TSS. Will I ever get it to work right or will I need to install the 73 turn signal switch? I have the new switch just need to install. What you u guys think?