Tap the breaks and things go crazy!
 

96 850 GLT. This just started. When applying the breaks, the radio volume fades up and down and sometimes cuts out for a second or two. I can hear the antenna going up and down. Also the SRS light flashes and the RPM arm will jump about 5k although the motor is not revving . I know this sounds like a short somewhere. The car runs fine it doesn't stall it doesn't hesitate. Sounds weird Right? Anyone ever experience this? Any help would be appreciated. Thanks.

sounds like something is going on with the ABS controller board or the ABS pump that is shorting and possibly putting voltage on a ground circuit. What happens if you turn the key to position 2 (engine off) and apply the brakes? What happens if you disconnect the connectors to the ABS pump/controller and apply the brake pedal (I believe these older cars can be driven with the ABS pump/controller disconnected so you should be able to do a quick test). For some research reference, google for some of the sites like Rocha-tek and Midwest ABS who rebuild the controller boards as they may have some content on symptoms etc.

You might also consider disconnecting the brake light switch and seeing what that does.

You may have a mechanical problem really, that is causing loss of ground on the I.P. cluster and generally everything in the dash. The brake pedal takes considerable force and so the dash will deflect when you use the brakes. Your ground wire for the dash may be loose. That is the most rational reason I could imagine that would send the radio antenna down. Good luck! I like working on wiring, but I know you probably don't.

+1 on the brake switch. My suggestion of turning the key to position 2 to see what happens when you press the pedal was my way of testing the brake light switch to see if its acting up. Also to the OP - check out Volvotips.com as you can find a wiring diagram for the 850 on that site.

mt6127: If I turn the car to the second position with the car off and tap the breaks I can hear and feel a clicking noise coming from the gear shift. Is that any indication or is that normal? All break lights are working.