I've read through a bunch of the 3rd brake light threads and have not seen my symptoms described:

The light has been out for a little while; was working when I bought the car in March 2017, but hasn't been for the last couple months. At least until the autumn weather moved in....

It works in the morning when it is cold, but after the car gets warmed up a little, it stops working.

Any thoughts as to whether this might be a connection-type failure (connects when cold and shrunken up, but when warm and expanded fails)? Or should I just go ahead and work on one of the several suggested fixes (well, except the OEM replacement part fix). Opinions welcome.

 

Yep, sounds exactly like an expansion/contraction issue from temperature. If it's never been taken apart and inspected I would start there, it's probably something just barely out of contact and the act of disassembly/reassembly will "fix" the problem.

 

If it's the one in the wing, it's the trunk to body connector.

 

No wing; on the shelf in the cabin.

 

Enough time has now passed to make a status report. I unplugged and removed the unit from the car, completely disassembled it, wiggled all the wires around including the two soldered connections to the board, reassembled, and during re-installation plugged and unplugged the connection into the socket several times (and wiggled the wire from the harness) before final connection and snapping it back to the parcel shelf.

Since doing that it has as far as I know been working consistently through cold weather and warm (including today's 75 degrees).

So fingered crossed.

 

 

Time for the denouement. Third brake light was failing again. So I decided to quit goofing with it. Today I went to the well and pulled out the LEDmarkers 3rd brake light module I bought just for this occasion (and bought just as they were completely disappearing following the apparent closure of the business...I got it on eBay from a guy that must have bought the remaining stock...he only had a few left).

Boy that thing is bright!