Brights have a mind of their own

[Yorkshire]

Well on the way home tonight the lights (only when using the high beams) started flashing on and off rapidly.

I replaced the multifunction switch already. That was my first thought.

[sly]

circuit breaker in the headlight switch itself may be getting weak.

[VicCrownVic]

So that makes a new headlight switch
and a new multifunction switch?


Do you use the lights only on the auto setting, or do you know if the problem exists with both auto and manual operation? (sorry if it was already asked)
If the headlight switch and multifunction switch are both new (assuming they aren't bad out of the box), and manual or auto operation doesn't make any difference then like gadget said, time to recheck grounds.
The one up front on the drivers side for the lights you said checked out as good, so next check the ground for the headlight switch. According to the 91 EVTM ground G102 will be located on the driver side and looks like it will be up by the spring/hinge for the hood bolted to the fender just like the one for the lights was. Check and clean like gadget mentioned earlier.

[Deno McThrash]

I had a problem like yours when I turned on my brights, they stayed on for roughly a minute and then flashed on and off until I switched back to my low beams. I wonder if this is similar? I've yet to replace anything

[Yorkshire]

I haven't looked at that other ground yet but if it were a ground, wouldn't the low beams be affected as well? Another thing is, when they start flashing I can hear a clicking sound in the steering column like a switch clicking on and off.

[sly]

since the circuit breaker is in the headlight switch... and is a thermal type, you could be hearing that clicking.

[VicCrownVic]

I haven't looked at that other ground yet but if it were a ground, wouldn't the low beams be affected as well? Another thing is, when they start flashing I can hear a clicking sound in the steering column like a switch clicking on and off.

Good point regarding the ground.
When mine were flashing on and off like that I could also hear clicking, click off, click on, click off... the clicking in my case I figured was a relay.
Also, as a side note, when the headlights would go out all the dash lights would go out on mine.

While my headlights stopped turning on and off on their own after replacing the headlight switch, I'm starting to wonder if that actually was the problem. Like yours, the new switch may have only helped but not actually fixed the root problem. I don't get to use the high beams in the suburbs of Detroit very often, except on very rare occasions, so the problem could still be there.
If the issue is a weak relay (auto lamp relay/headlamp control relay) in the system, this could explain why only high beams behave as they do. So perhaps the headlight relay harness I made and installed is the reason why mine stopped having the headlights turn on and off. Since the new relays take the load off of the old tired relay(s).

If my theory is correct that it is a weak relay (or whatever other component), then perhaps the headlight relay harness mod could be your answer.
If you do the mod and it doesn't correct the issue, at least you are one step closer to sparing the new switch you installed from the stress of high beam load.
However, if the issue does go away after doing the headlight relay harness mod, then perhaps there is something to my theory and I probably still have a weak relay/component in my system.

[Yorkshire]

I've had problems with my dash lights for some time now. For the longest time they were off, now they're really dim on the speedometer and radio and the lights for the ATC are off. I was planning on doing the relay anyway so I'll do that sometime when I have a little cash and spare time and get back with you.