1991 FORD THUNDERBIRD

The links suggest it doesn't have one and to check the 'dimmer switch' whatever that means.

https://www.google.com/search?q=1991+Ford+F-250+headlight+relay+location

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check for a faulty light control module or a faulty light relay

headlight switch is bad

the hazard switch is on the steering column a little of to the right ( like the 1 O'clock position) the relay for the flashers is under the dash on the drivers side, towards the kick panel.

It is your flasher relay switch. I had the same issue, and that piece is under the dash on the drivers side. The flasher relay switch is a little black box and I got it from my ford dealer for about 60 dollars. :)

I had the same problem it is your light switch. that is right behind your little switch next to your dash that you pull out. Refer to maunuals on how to take it out and replace it.

SOUND LIKE FAULTY HEAD LIGHT RELAY.

Here is the recall info.

The vehicles affected by this recall are certain ‘92 & ‘93 model year Ford Thunderbirds and Mercury Cougars. The problem; the headlights turn off, then come back on after driving with the fog lights on. Ford is replacing the headlight switch and if necessary the electrical connector for the headlight switch. Repairs for a safety recall are to be performed at no cost to the vehicle owner, even if you are not the original owner. In addition, if the headlight switch was replaced before the recall, the owner is entitled to a refund for repairs. But the owner should still bring their vehicle in for inspection. Why? The replacement part may not have been of the new design.

Check all fuses and relays but sounds like a overheating headlight switch...Good Luck

waz up i have a 1992 thunderbird and my headlights did the same thing check the turnsignel switch were the highbeam and low beam switch is if it is bad like mine was the connecter on it is prob burnt ford had a recall on that when that switch goes bad it melts and gets hot and brns the connecter and makes the wireing over heat and it makes the headlights go on ond off hope this helps