Simple electrical question has me stumped...
 

I am trying to hardwire my Passport 8500 radar detector directly to my car so I don't have to use the cigarette plug. I have double and triple-checked my connections (it uses a simple 4-wire telephone cord), yet something is preventing the unit from working.

When I test the OEM "cigarette plug" cable, I get the following:

BLACK: Nothing
RED: Ground
YELLOW: -12v
GREEN: -12v

When I test my hardwired plug, I get the following:

BLACK: Nothing
RED: Ground
YELLOW: 12v
GREEN: 12v

Why does the OEM plug make it 12 volts NEGATIVE? How do I get mine to be negative? Does that make a difference?

Thanks!

- Mike

switch the red and either the yellow or green around. apparently the red is your positive, and yellow or green is negative, I'm thinkin'.

btw, you could just solder some spade connectors to the old cigarette plug, that way you get the correct voltage drop. Otherwise you could blow out the illumination on your Passport, and that would p*ss you off pretty good.

Hmmm...

You may have something there.

I will try it with two wires directly on the battery. I will hook them to the ammeter and see if the "charge" switches positive to negative when I flip them back and forth... I think it will.

Back in a few minutes... SmileWavy

no no, I meant put the positve test lead from your tester on the red wire, and the black negative on the green or yellow. It sounds like you hooked it up correctly.

Most items like that are rectified with a diode so you don't blow the unit if you plug it into a negative earth car, like older British.

Bingo! :D

If I swap red to black, and black to red, I can change the polarity off the voltage!

Let me rewire the detector and see what happens. I have been banging my head on the steering wheel for two hours over this before I decided to post. :mad:

Also be sure to look at the bottom of your radar detector for the correct voltage. You don't want to run a full 13v to that thing.

Actually, it works now.

I had the ground and power leads swapped. When I switched them, the readings on the contacts were perfectly correct (I still don't know why).

Thanks!