I had the same problem on my 1995 940 wagon. Beleive it or not, the lamp fail sensor failed and cut off all my brake lights. What happens is when the brake is pressed, the brake light swith turns on. The wire from the switch goes to the lamp fail sensor where it is split into three signals, on for each of the two side brake lights and the third for the one in the rear window. The brake fail sensor checks that current passes through all three lamps. If not, it activate a warning lamp on the speedo indicating that a lamp has failed.
The problem in my case was that the solder on the lamp fail sensor developed a dry joint where the wire from the brake switch entered the sensor, before it was split into three.
If you are good with a soldering iron you can resolder all the joints and your brake lights will work again. Otherwise replace the lamp fail sensor. It is a very large, round, Red relay about two inches high and about an inch and a half in diameter. It is located with all the other relays behind the fuses in the center panel behind the ash tray. Good luck
Sunday, July 26th, 2009 AT 11:59 AM