I have a 1990 Ford Thunderbird Super Coupe that I am considering selling but I want to fix an issue with the headlamps. On occasion the headlamps will flash randomly when I turn the fog lights on. I switch to the high beam and sometimes the lights will come on again and sometimes they wont but when I pull the stalk to the flash to pass position the high beams always come on. If I turn off all the lamps they will come back on again once I pull the switch out. Is this a sign of the relay failing or dimmer switch failing? Any thoughts?
Relay failure?
- Thread starter bds1984
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It helps to have a wiring diagram. This way you can figure out the point in your wiring system that is common to the failures you are seeing.
My experience is that relays fail intermittently before they totally die. If the relays related to the high/low/fogs are the same, switch them around and see if that changes your failure modes. If so, you'll know if you have a bad relay. Then you can pull them out and test them to isolate the bad one. If they're cheap, you could just replace them and see if that solves the problem.
My experience is that relays fail intermittently before they totally die. If the relays related to the high/low/fogs are the same, switch them around and see if that changes your failure modes. If so, you'll know if you have a bad relay. Then you can pull them out and test them to isolate the bad one. If they're cheap, you could just replace them and see if that solves the problem.
If the T-bird electrical system is anything like the Mustangs of the same era then you will likely have a wiring/connector issue. Ford did not use relays in the head/fog light system of the Mustang leading to burnt/melted wiring and connectors on the GT model due to the excessive current draw with the fog lights. The popular fix with the Mustang is to add a relay into the fog light circuit.
Bear in mind the feds have a law about no high beams and fog lights at the same time. So this forces makers to wire a car so the fogs are killed then.
It is common to run them off the parking light draw so you can use them with parking or low beams, but this would need a relay to kill them on high. But yeah you need a diagram. Ford uses a thermal doohickey in the regular headlight switches that has been known to go bad.
It is common to run them off the parking light draw so you can use them with parking or low beams, but this would need a relay to kill them on high. But yeah you need a diagram. Ford uses a thermal doohickey in the regular headlight switches that has been known to go bad.
Thanks for the info. Shortly after posting this I noticed no relays anywhere except for the fan and horn. I am leaning towards the headlight switch failing because when the lights go out I don't even get high beams to light up. Now the only problem I have now is to remove the darn knob from the switch without ruining the dash bezel! Any advice on that?
I don't have any info on the '90 model, but for '92 the knob just pulls off.
I thought that is how they came off. Any other Ford I have worked on where I had to take the dash apart and headlight switch off, the knob would just pull off once a small screwdriver was inserted in the back side of the knob. It is almost like this one was glued in place with superglue!
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