This is a 1990 Trans Am GTA, with the foglight switch above the radio (NOT the earlier model with the fog light switch to the left of the steering wheel).

If I turn on parking lights or headlights (low beams) then I can activate the fog lights by pressing the fog light switch. But as soon as I release the switch (it's a momentary) the lights go off.

Both bulbs are good. I've changed relays. Same behavior.

Fog lights won't stay on.

Factory wiring seems to be intact / unmolested. 20 amp fuse is good.

It's been 20+ years since I last had a car with this type rocker switch. Is it supposed to be a momentary press that springs back? That's what I seem to recall. Or is it intended to somehow stay pushed until you push it the other way?

My other cars are no help. The 86 has the older style foglight switch and the Firehawk is just a Formula, so no foglights or switch.

So what happens if you remove the wires from the back of the switch and bridge them?

The lights stay on.

The fog light switch is a on/off, when you flip it to on, it should click and lock to the on position. Little green light should come on when the switch is on and the headlights or running lights are on.

There are 5 wires to the back of the fog light switch. The Brn+Yellow are connected to turn on the fog light relay (by the fuse box). The other three wires are for the dash illumination, and to power the little green light when the fogs are on. It is possible to accidentally jump the connector so the fog light relay is being activated by the dash illumination. You don't really want to do that.

If the switch is clicking back, are you sure its a foglight switch and not a rear defrost switch? Defrost has an orange light. Should be easy enough to find a good used switch on Ebay. They're a lot easier to find now than they were 15 years ago.

Yup, it's a foglight switch alright. Green light. But it behaves like "half" a defrost switch in the respect that it is a momentary press. It's not like you press it on the right side and it stays snapped down until you press it on the left.

Easy, yes. Inexpensive, hardly. But I guess that's the next step!

Well, bad news. The problem was not the switch. I just got my "new" switch for $40 and it doesn't behave any differently.

There are 2 good, working lamps, I've replaced the relay, have replaced the switch. Any other ideas on how I might track this down?

My 91TA has a rocker type switch. From your description, I would have bet on the switch being bad. You might want to try getting the rocker type from the 91 model year. It should fit in the same location and wiring "should" be the same.

Hmm, so the new switch doesn't click and stay snapped to the on position? Because it should, it's a rocker switch, not a momentary contact switch like the hatch release and defrost. It should make an audible clack and stay in position, green light should light up and stay on until you flip the switch off.

Yep, that's the way mine is set up Drew. 1990 should probably be the same. It is not a momentary switch as was described. Probably a PO mistake a few years back and he did not care.