I just got back from driving today, I took the IROC down the highway and for some reason the third brake light wont go out. It is a 1988 with the 5.7. I am not great with wiring, does anyone have ideas as for where I can start?

 

Your brakelight switch has two sets of contacts, one set for the regular brakelights and one set for the third brakelight. Since they are not all on, just the third one is, it's likely not gone out of adjustment, but it'd be an easy check to make sure it hasn't slightly slipped out of position. If it is still adjusted properly, then the contacts that run the third brakelight have become fused together, a somewhat common problem with these. If so, it'll need the switch replaced.....

 

Thank you for the reply, I will check this weekend and see if I can get it out.

 

What a weird design... Now for the 80's GM question of the day, was that by design, or to save money?

By Design Argument: The third brake light exists in case one or multiple lights fail! However, the contacts failing could be one way for the light to fail. Ergo, two switches so that the third brake light works even in the contactor failure scenario!

Save Money Argument: We have all these harnesses for two brake light cars, but we have to put a third on now... Just, like... bolt it on there or something... It'll be fine...

 

Hi codyman,

Very good question indeed, however I don't know GM's motivation for wiring it that way. I only know about the dual switch deal because over the years I've run into every combination of possible failures these switches can have, and my wild azzed guess has always been that on the cars where the brakelights are also the turnsignals (Trans Ams I think) having the third brakelight as it's own separate circuit would make for one less set of contacts needed in the turnsignal switch.

Or not......

 

The One Switch that has 3-Terminals for a Stop-Lamp Circuit and a CHMSL Circuit were created so that the Switch could be used in a multitude of GM Car Models.

Some Models do use the same Bulb for Stop and Signal/ Hazard...thus require a separate Circuit for the CHMSL.

If not done this way the CHMSL would Blink with a Signal/ Hazard ON.

 

A short update, I pulled the brake switch out to look at it and as soon as the plug came out, I could see it was all melted inside. Ordered a new one from rockauto, installed it and now everything works well again. Thank you all for your help