1988 420 SEL Cruise Control not working

Was working when I got the car 2 weeks ago. I've had a radio installed since then. Is there something behind the dash that could have been disconnected. Where else should I look assuming the radio install has nothing to do with it.

Thanks

[420SEL]

Possibles are the actual control lever that operates it, the cruise amplifier (located under the dash I believe), there is also some connection to the speedometer, and occassionally the wrong voltage bulbs in the rear brake lights with cause a malfunction,as operation of the brakes will interupt the cruise (signaled by the lights coming on). I doubt there is anyone who has owned these cars and has not had trouble with the cruise. Best bet is the amplifier - the soldering cracks.