Volvo: 93 940 Shift + Brake light problem, wire colors, shift lock

Question
My wife drives a 1993 940. The overdrive (fourth gear) would work intermittently. Finally, it stopped working all together. I figured that the switch or wiring in the shifter handle had become broken. I opened the center console and tried to look and see the wiring or wire colors, I had thought that if I could just jump them, I would be able to diagnose or rule out the switch as the problem.

Well... The shifter assembly doesn't take kindly to dissasembly/inpsection. I can't even get the cover off (the shift indicator panel (PRNDL) seems to not be able to lift off)! Needless to say that I was NOT able to access the wiring or jump the switch. In the process the shift lock override button dis-appeared (apparently it fell into the "well"). So, I closed everything up, and now the cars brake lights won't work! I have checked the fuse (#4), for 12V at the switch, for a bad switch, for burned out bulbs, etc... All is ok.

Is there a connection between the brake lights and the shift lock switch? Is there a common problem with the overdrives? Maybe the switch or a relay, etc...?

I thank you in advance for any help you can give me.  

Answer
The typical failure on these cars is the overdrive relay, a small box burried in the dash board that takes the signal from the overdrive button and sends current to the overdrive solenoid on the transmission.  That relay, being a mechanical device, is the culprit 95% of the time, not the button, so unfortunetly you might have been barking up the wrong tree.  A simple replacement of that relay (usually $40 or so) will fix the issue.  As for the brake lights not working, I can't offer a specific cause, but I suspect that you are grounding part of that button circuit in the shifter knob that is tied to the brake lights, thereby shorting the whole system.  You probably need to fish the button out and properly mount it.  I bet that will fix the problem.