Headlights - 1990 Tbird Supercharge, only 64,000 miles

ford
thunderbird

#1

I’m hoping somebody can help me with this, sorry if it’s a long story. Every now and then my headlights dim, flicker, and then go out. They will come back on only to do it again a few seconds later. It’s only happend 4 times. After the first three times (all while driving on a freeway that was having work done making it but bumbier than usual) I took it to the shop. He tested the electrical sytem and could find nothing wrong. While he had my car he replaced a bad spark plug that had come off and fried a spot on the boot. I know the two things aren’t related but the lights were fine for the next two months. The other night they did it again while I was on a very dark back road and it scared me to death. This road was a little bumby and very curvy. I’ve had the battery and altanator checked and they are both fine. Any ideas?


#2

It appears that there is a bad connection to power for the lights. The trouble may be with the switch or in the wiring before or after it. The relay is in another suspect also. You may be able to locate the trouble by watching the lights and tapping on suspected trouble spots using a screwdriver handle.


#3

Thank you. I was told by a couple of people that the relay might be the problem but then a guy told me if so, it would just go out not act up now and then. I drove around yesterday with the lights on trying to get them to do it - finally near dark (and going on bumpy roads) they did. I noticed a hum coming from where the relay is located every time they started to dim and go out so I think you’re right. Does that make sense to you?


#4

It sure does. By listening for the buzz it should help you locate the relay if you don’t already know where it is under the dash. You may be able to prove it is the relay by tapping on it and checking for a change it the lights. Relay switch contacts can get dirty and pitted over time and cause the kind of trouble you are having. The contacts can heat up due to the bad connection and that causes more resistance which drops the voltage available to the lights and they dim.


#5

Thanks again. I’m going to try that right now. One more question. My friend thinks it’s my actual light switch. I don’t agree because nothing changes when I wiggle the switch. If I try your tip about the relayI guess I’ll answer my own question but does the switch sound like a problem to you?


#6

While it is possible the problem could be with the switch I doubt it is, your friend could be right though. The trouble could also be with the relay control circuit that ties to the relay coil. A faulty circuit could make it buzz which usually means the contacts are switching at a rapid rate also. The light switch would control the rely coil circuit.

Usually when relays buzz the trouble is due to a problem in the wiring that causes the voltage to the coil to drop down like a near short circuit condition or a high resistance in the lead. Either way the voltage to the coil drops down and the relay turns off. Then the supply voltage goes back up and the relay closes again. The cycle continues on like that. Since your lights are going out for a bit it may mean a circuit breaker is tripping and then resetting and the lights would come back on again and go through the same cycle.


#7

Ok, I give up. I was told the relay should be right behind the headlight switch. I replaced the switch but for the life of me can not find the relay. I’m not the ony one either. About ten people, including two who work for Napa, have looked. It’s not in any of the usual places and if it is behind the headlight switch I would like to replace it while I still have that part of the dash off. Do you, or anybody else, know where it’s located?