1994 Tailight Problem
- Thread starter rpm427
- Start date
79jasper
Chickenhawk
Sounds like a grounding problem.
That's what I thought but the only ground that has give me trouble in the past is the one below tail gate lip on drivers side and I cleaned it and reassembled with no difference?
Check the connector that hooks the farm wiring harness to the bed wiring harness? There is also a ground somewhere near the back on the drivers side frame rail. I would check there also. Really sounds like the ground is an issue.
GOOSE
Happy IDI'er
Your turn signal switch may need replacing.
What switch are you talking about by the way.......
Brake light issues can stem from the turn signal switch, tail lights would most likely be the headlight switch. I'd double check both. Wire harnesses can melt adjacent to the headlight switch because the full headlight current passes through the wires. That is why many do the headlight relay mod.
What switch are you talking about by the way.......
Brake light issues can stem from the turn signal switch, tail lights would most likely be the headlight switch. I'd double check both. Wire harnesses can melt adjacent to the headlight switch because the full headlight current passes through the wires. That is why many do the headlight relay mod.
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Turn signal switch is 8 months old as emergency flasher stopped working and that fixed the problem.The switch I'm talking about is light switch and it's about 9 months old as I replaced it also while looking for this problem.I just need to know where these wire connections and grounds are and not a idea as I can look around but would be nice to know exactly where you go?
Lithgow
Full Access Member
I had the same problem, turned out to be the connector that plugs into the headlight switch. It has nine wires, and the one to the tail lights was all burned and charred looking. Oreileys had the connector in stock. I looked on youtube first, to watch a video on changing the headlight switch, and it turns out the guy had the same problem as me, a charred connection for the tail lights. (he was doing it on a 93 bronco). I saw a tech write up somewhere about installing a relay so that all the amps don't have to flow through the switch. I plan to do this soon. It looks very easy to do and only cost a couple bucks. A headlight relay is also a good idea. I think it was on another Ford forum. Hope this helps.
Your problem is definitely a grounding problem, but finding where it is may be difficult. It starts with the ground connection at the bulb and the socket. Then as was mentioned, may go through several connectors till it finally is bolted to something metal.
The brake lights and the running lights both share the same ground in the dual filament bulb. If that ground is bad, the brake lights will find a new ground, letting power go up through the running light circuit in reverse till it finds a path to ground somewhere through a component up front in the wiring harness. But when you turn the headlights on, power is now running back down the running lights circuit, butting heads with the power from the brake lights. All kinds of crazy things can happen with a poor ground.
Sometimes the quickest way to solve a grounding problem is to run a new ground wire from the ground wire at the sockets to a good place on the frame. Then make sure you have a small ground wire going from the frame up front to the neg battery post.
The brake lights and the running lights both share the same ground in the dual filament bulb. If that ground is bad, the brake lights will find a new ground, letting power go up through the running light circuit in reverse till it finds a path to ground somewhere through a component up front in the wiring harness. But when you turn the headlights on, power is now running back down the running lights circuit, butting heads with the power from the brake lights. All kinds of crazy things can happen with a poor ground.
Sometimes the quickest way to solve a grounding problem is to run a new ground wire from the ground wire at the sockets to a good place on the frame. Then make sure you have a small ground wire going from the frame up front to the neg battery post.
The cruise control brain has a terminal hooked to the brake light circuit. If it sees voltage on this terminal, it assumes you are hitting the brake pedal and the cruise control turns off. Like I said before, with a bad ground the voltage from the lights will try to find another path to ground. So the voltage from the running lights is running up backwards through the brake circuit, finding a ground somewhere. This voltage running up backwards is fooling the cruise control into thinking you are pushing on the brake pedal.
