I had constant problems with taillights especially brakes. Intermittant problems. Finally looked at the area where the plug on the wiring harness connects. Used a mirror to look underneath, and saw that the circuit board was worn out, and had permanent depressions from the contacts on the plug. I took the light assembly out to fix it.
I took a sharp Utility Knife, and whittled about 1/8 inch off the face of the plastic rib where the circuit board wraps over it. The part of the circuit board that wraps over the plastic rib becomes detached, but it is unimportant.
Be careful to work slowly and don't deform the area of the circuit board that has the contacts. The idea is to whittle away the "worn-out" area of the circuit board, and the rib it is up against.
The plug then slides on further to a new contact area of the board. I wrapped a wire tie around the tab that retains the plug, which made it hold the plug in further.
Just like new, and I expect to have no trouble for another 160K miles.

Hope this helps someone else!