PM brake light/motor not coming on

[MSDGN]

This is for a friend...87 GN with powermaster...pump the pedal to relieve pressure and turn the key on...the brake light doesn't come on and the PM motor doesn't cycle...here's the strange thing...if you push the emergency pedal down the light comes on and the motor cycles...can also get the light to come on and motor cycle by grounding one of the wires in the PM pressure switch weatherpack connector...can't remember which one of the wires...he is getting 12V to hot wire in the switch connector...pressure switch was replaced with brand new one...same problem...this just started happening all of a sudden...sounds to me like a wiring problem...maybe an open circuit somewhere but I'm not an electrical expert...this guy has been doing some things behind the dash...he has the upgraded dash similar to the GNX one with all the guages...he recently installed an alcohol system and had the dash panel out so he could tap into the boost line...maybe he knocked a wire loose...need some help here as he is trying to get the car ready for Vegas Natl's in a week and a half...

Please don't respond to this if your only answer is "switch to vaccuum" as that is not an option...need some ideas where to look for the problem...

 

[FastTurb]

lost ground - anybody see it??

yep that wire on the switch must have its own ground for the motor to run. you can jumper to it or even jumper on the motor connector. If you run a line to the case of the motor to ground it will probably work too. I guess the motor is isolated enough through its mounting that it needs the ground reference that is attached and run through the switch. after years, weather etc the original ground goes bad. either fix it or run your own. You sure don't want to spend $200-600 for a new PM and find out it doesn't work either and it was just a ground wire.