What to check? What to do? Any suggestions would be greatly appreciated.

My 86 had the connector above the halo, check that for voltage. Do you have brake lights? Not sure if on same circuit. If you have voltage at the connector it might be the bulbs.

Bob

If it's a targe, make sure the cables are attached to the hatch strut rods.

Yes I do have brake lights. I will check this out tonight.

Great! I will check this out too.

"If it's a targe, make sure the cables are attached to the hatch strut rods."

I don't know what that has to do with the brake lights. The third brake light runs of the same circut as the main brake lights. There is a light blue wire and a black wire that run to the upper light. check them for power. You may have four out of commission bulbs up there. The corvette catalogs sell them for 11 or 12 dorrers each. I found a place on the net that sells 2 for 6 dollers. 12V 20 watt halagen.

So this wouldn't be a typical bulb I would be able to find at a parts store?

You might be able to, not sure. Years ago when my bulbs burnt out I was shocked by the dollers they wanted. I went to Radio shack and bought some cheap bulbs 1.49 each so I could pass my state (NY) iinspection. I had them in for years before I relized how dim they were. That why I am puttin the proper ones in. I also wired in a devise called BackOff the will blink the upper brake light when you step on the brake. This is another thing this in the corvette catalogs the you can get from the sourse at half the price.

Had the same problem on my 90, possible the switch on the brake
peddle, about $8 at dealer good luck.

When my 3rd brake light didn't work but lower set did (89) it was my switch by the brake pedal -

Mine also, but got the switch a NAPA or one of those stores for about $6. Easy to replace as long as you are not 6 ft tall weighing >200 lb and are still flexible enuff to bend like a contortionist.

I actually have the reverse problem - third brake light works like a charm, mains do not. I was told that the cyclops light was controlled by a completely different means than the mains, and that the mains were controlled by the switch behind the pedal - is this true?

The brake switch is a DPST that delivers power to two separate circuits when the brake pedal is depressed:
-one is to the Turn/Hazard Sw Assy to activate the regular stop lights
-the other delivers power directly to the high level brake light.

Ditto that Vettesareme....I had the same problem and it drove me nuts because you'd think that if the brake lites work then why DOESN'T the 3rd brake lite work? Well, one of the contacts on the brake lite switch directly go to that lamp and when I replaced it..........the 3rd brake lite worked again.........just a pain in the **** working on your back, wedged between that sill and seat. cheap, cost me around $7 for the switch.....good luck.

Thanks Everyone! I will look into all of these possibilities.

If it is those bulbs, GM charges 12.00 ea. M. A. is about 8.ea you need 4 of them and they are halegens

Sorry to resurrect an old thread but I just had the same problem with my 3rd brake light not working and it was the brake switch. Just replaced it. All good.