Our latest Volvo, Hedwig, came with considerable amount of things not working. We got her late Fall and I did my best to get things roadworthy for our harsh winters up here. One problem's been two of the five lights in the rear tail light assembly would not light. I'd be wiggling and twisting the bulb holder to make connection.
Volvo came up with this flimsy circuit board to direct voltage to the rear lights. The bulb for the running light and brake light was one of the offenders. I found a small chunk of the circuit board gone for that particular bulb.
I found a replacement circuit board on line, and ordered it.
When it arrived, I removed the tail light assembly, unhooked the circuit board wire harness and the ground wire, and brought it in to the bench. I removed all the bulb holders and bulbs, a seal, and got a better look at the circuit board. I got the old one off, and started to replace the new one. At each bulb socket, the circuit board fitted over three small plastic pins to secure it. When I got the the bulb socket for the rear light/brake light, I found that the pins were melted away, and the area under where the board overheated and burned. When I got it back on the car, sure enough, my one bulb would not light, even with the new circuit board. I got my test light out, and poked the wire harness till I located the running and brake lights. Taking the bulb holder inside, I drilled smalls holes for soldering lead wires to the two tabs for each filament. Back on the car, I cut the two wires back a few inches from the circuit board harness, and added my new lead wires and secured the connections with wire nuts. Bingo, the lights all worked on the right rear side! But not the left rear side! I could force the light to work if I pushed the back of the bulb holder tabs. I looked close at the left circuit board, and it looked old and cracked. So, I repeated my process on the left side and now all the lights work great. I reckon after 23 years, you gotta do something about those thin ole circuit boards.