Help; I installed a cigarette lighter unit to my 36 pickup so as to use a GPS and the GPS will not power up. My voltage meter shows 12.5 volts, so I got out the voltage tester and the tester bulb shows up in red. I thought perhaps I wasn't getting a good ground so I ground to the starter, the motor and the frame and still will not show green. I tested my other cars and they show up in green. so whats the problem? I know the GPS is good because it works in my other cars, Help!!! THanks;...Richartd