Tail Light Wiring Question

[gerlbaum]

I was just curious if anyone has dealt with this before (nothing in the search showed up). This is on a 87 F250. I have not checked anything with my multi meter yet but I will this weekend. Let me know if you think I am on the right track:

My turn signals, hazard, back up and brake lights all work fine when the headlights are off. When I turn on my headlights both tail lights should light up. My right rear does not. In addition, while the headlights are on, the right rear brake light and turn signal light do not work. Hazard lights work fine. All other lights work fine with the headlights on.

The left rear works perfectly. I am thinking the socket is at issue? The color of the wires to that socket appear to be a orange/lt blue, black, and the third was hard to see but was either a dark blue or another black wire (it was at night).

Appreciate any other ideas.

 

[IDIBRONCO]

I think the socket would be a good place to start. It sounds like how a bad one can act sometimes.

 

[gerlbaum]

I think the socket would be a good place to start. It sounds like how a bad one can act sometimes.

Thanks. I just got a power probe off eBay so it will be a good time to play with it this weekend and, if I'm lucky, accidentally electrocute myself! I'm an electronics moron.

 

[gnathv]

You’ll love that power probe. Handy to use.

 

[Thewespaul]

Which power probe did you get? I love mine. Let me know if you need any schematics or help once you get to look at it.

 

[gerlbaum]

I got the probe II only because I got it for cheap. I wanted the III but they were pretty expensive. Unfortunately it doesn't come any of the additional attachments.

Side note, Ron Francis has a bunch of 1988 and earlier Ford truck stuff; all gas but I hear a bbf engine harness is very close to the diesel. He also has two complete rewire harnesses - one more stock and the other more for a custom rewire.

Replacement harnesses
https://www.ronfrancis.com/products.asp?dept=296

"Stock"ish rewire
https://www.ronfrancis.com/prodinfo.asp?number=XP-725

You must be registered for see images

Customer complete rewire
https://www.ronfrancis.com/prodinfo.asp?number=AC-67

You must be registered for see images

 

[cason234]

In case you didn't get the tail light fix you were looking for...... I had a similar circumstance a bit ago, and I found the plug on top of the steering column (for the turn signal switch) was loose. I took it apart, cleaned everything up, and put a little di-electric grease on the contacts, and my tail lights work just as they should. NOTE: this is the crescent shaped plug that connects the wiring harness of the body to the steering column that controls turn signal / cruise control / horn wiring). Hope that helps!

 

[gerlbaum]

Thank you. I'm gonna tear in to it this Saturday. I'll update with my successes or failures. I scored some oem sockes so they'll be going in regardless to replace my corroded ones.

 

[gerlbaum]

New socket cleared it up. Note, when wiring the new one in make sure to wire the black to ground and not the brown wire which is very dirty and looks like it's black.

 

[Thewespaul]

Glad it was a simple fix

 

[IDIBRONCO]

Me too. Isn't it absolutely CRAZY what will happen with a bad socket? After I did the IDI swap on my Bronco, I ended up replacing almost every socket on the stupid thing. It was frustrating.

 

[gerlbaum]

Glad it was a simple fix

Haha me too. I suck as wiring

 

[gerlbaum]

Me too. Isn't it absolutely CRAZY what will happen with a bad socket? After I did the IDI swap on my Bronco, I ended up replacing almost every socket on the stupid thing. It was frustrating.

Especially when you have a moron (me doing it). I always screw up the litle things.

 

[franklin2]

Your problem was a bad ground to the light. The ground goes from the bulb to the socket, and then the socket to the wiring harness, and I think it might go all the way back up front to the body. It is common for the ground connection to get corroded in the socket.

Those bulbs back there are dual filament. One filament is for the turn/brake and the other is for the taillight. Your brown wire goes to the taillight filment, the colored wire to the brake/turn filament.

The two filaments are tied together on the ground side on the bulb itself. On the older trucks it was the brass part of the bulb. From there they find the return path to ground and the neg of the battery.

If any part of the grounding circuit is bad, what happens is when the headlights are on, voltage is sent down the brown wire to the taillight filament. It goes through the filament, and then when it gets to the ground it can't find it. So it searches for some place to ground, and it will go backwards up the brake/turn filament and backwards up the wiring to the front of the truck till it finds a place to ground at. The taillight burns, but if you look carefully you will notice it is dimmer than it should be from the poor ground it is finding in the other circuit.

When you press the brake or activate the turn signals, they will not work because the voltage they send down their wiring bumps heads with the voltage going backwards from the taillight circuit, so 12v on both sides of the bulb makes it go out.

Anytime you have crazy things like that happening with a vehicle bulb, suspect a grounding problem.

 

[snicklas]

Your problem was a bad ground to the light. The ground goes from the bulb to the socket, and then the socket to the wiring harness, and I think it might go all the way back up front to the body. It is common for the ground connection to get corroded in the socket.

Those bulbs back there are dual filament. One filament is for the turn/brake and the other is for the taillight. Your brown wire goes to the taillight filment, the colored wire to the brake/turn filament.

The two filaments are tied together on the ground side on the bulb itself. On the older trucks it was the brass part of the bulb. From there they find the return path to ground and the neg of the battery.

If any part of the grounding circuit is bad, what happens is when the headlights are on, voltage is sent down the brown wire to the taillight filament. It goes through the filament, and then when it gets to the ground it can't find it. So it searches for some place to ground, and it will go backwards up the brake/turn filament and backwards up the wiring to the front of the truck till it finds a place to ground at. The taillight burns, but if you look carefully you will notice it is dimmer than it should be from the poor ground it is finding in the other circuit.

When you press the brake or activate the turn signals, they will not work because the voltage they send down their wiring bumps heads with the voltage going backwards from the taillight circuit, so 12v on both sides of the bulb makes it go out.

Anytime you have crazy things like that happening with a vehicle bulb, suspect a grounding problem.

I was behind a really nice OBS Bronco doing this last night. His tail lights seemed ok, but when he would step on the brake, both backup lights lit up, dimly, the drivers side light went out completely and the passenger light was a bit brighter than it was before he stepped on the brakes. I made a comment to the wife, "He has a ground problem"..... she laughed and agreed. My guess it was something in the drivers side light.....