Volvo: 1990 Volvo 240 break lights, volvo 240 break, volvo 240

Question
I noticed that my breaklights (1990 240 4-door volvo sedan) were not working a week or so ago.  At first I thought it was a problem with the conector so I cleaned off the PC board and the lightbulb housing but that didnt seem to work.  Actually when I inserted the lightbulb and housing into socket (left/drivers side) the break light flashed on along with the 3rd break light in the rear window and was accompanied by a electrical noise like a spark, but when I twisted it into place (so as to lock it in) the light went off.  Meanwhile the right side break light was not responding at all.   After this exercise continued, the left tail lights stoped responding all together including the running tail lights.  The right side continued to be responsive to everything but the breaks (no break lights).   At this point I noticed that the part of the pc board (left/driver side) that connected to the gang connector (wire cluster) was partially melted and pieces had broken off.    Thus, I decided to drop the $70 and buy a brand new left tail light assembly with new pc board, light fixtures and bulbs, which I installed this week.   As it stands, neither side's break lights are working, the left and newly installed side works only for the blinker and the reverse lights.  The right side works for the bottom two running tail lights, blinker, and reverse light but not for break lights; that is, on the Left newly installed side only the blinker and reverse lights work while the on the right side only the break lights dont work.
HELP!! Im a poor grad student who cannot afford excessive mechanic fees.   Also I noticed that the lightbulb dash indicator responds when the lights are manually turned on but NOT when head lights are off and I apply the break pedal.  

Answer
A lot of times water can get into the plastic tail light assemblies and rot the ground connectors.  There should be at least 1 per side, usually bolted right into the chasis somewhere close to the light, usually on the inside.  This issue sounds like a classic decayed ground problem, and will involve you maticulously tracing all wires, especially grounds, looking for partial shorts of that nature (sometimes they can manifest themselves as rusted bolts, or green corroded eyelets at the end of ground wires.  You should have to spend any more money tracking down a problem like this, other than your time to track the short, and the money to replace a few bulbs once you thing you've found it.  Good luck!