Cadillac Repair: Brougham cruise control, ground circuits, wireing diagram

Question
My 1990 Brougham (5.7l) cruise control shuts off completely a minute or two after engaging.  That is, the power light goes out as well as the "set" light.  After 30 seconds, the power light comes back on, but memory is lost.  If the cruise control is reset, it will again engage, then shut off, usually sooner. The actuator has been replaced with no change in behavior.  Can you suggest where the problem lies?

Answer
Hi Linton, If the cruise just disengaged by itself but the power light remained on I would say you have a problem with the brake switch. But since the switch appears to loose power like you turned the switch off it looks like you could have a bad switch, a loose connection behind the switch or somewhere in the power or ground circuits that feeds the switch.

     What I would do is get a wireing diagram and remove the switch from the dash. Then determine which wire is the power wire to the switch and install a voltmeter or 12 volt test light into that wire and ground. Drive the car and when the cruise quits see if power is still getting to the switch. If it is then put the meter/test light on the ground wire and somewhere that is a power source like the cigar lighter useing an adapter and repeat the drive. If you have power and ground to the switch but the switch goes dark then replace the switch. On a couple occasions I had a bad switch you could see where the switch was starting to separate the back panel from the rest of the switch housing.

    Hope that makes sense and gets your cruise working again. Let me know if you need anymore help. Bill