Finally replace my switch. Taillights been erratic for months.
Have a Haynes manual, and read a few threads about how to.
Biggest problem was the electrical connection under the dash. Instructions only say "after blah blah, disconnect harness". That's it. There should be a tutorial on the harness connection. Where it is, how to remove it from the clip holding it up so a person can work on it, how that connector comes apart, etc. Should include pictures. Probably on a work bench, since getting decent pics under the dash woud be futile.
AND, the switch itself is a 'discontinued' item (forgot the word the partsmgr used). Dealers can sent it back or whatever. They gave me a really nice discount (about 80% off list) because of that. Doesn't hurt to ask.

 

So the old switch was faulty? And all your Monte's tail lights and brake lights work as they should now, with the new switch? (I ask because my third brake light isn't working.)

 

Yeah, all seem to be working. The third light works off the right taillight. At least on mine both center and right would work or not work at the same time. Check those bulbs tho.
Also, my turn signals would work erratically. The left rear would blink twice too fast while the left front wouldnt blink at all. But if I wiggled the lever, then it worked OK.
The switch was the ONLY thing that could cause my problem.
I can see on my old switch that a couple contacts are worn out.