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Automotive Monomaniac
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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
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2018 - Porsche 911 Carrera 7MT / 2018 - Porsche Macan 7DCT / 1993 - Cadillac Allante / 2023 - RAM TRX (on order) |
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03-17-2007, 04:54 PM
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Join Date: Oct 2004
Posts: 15,612
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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. |
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03-17-2007, 05:11 PM
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Automotive Monomaniac
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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... 
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2018 - Porsche 911 Carrera 7MT / 2018 - Porsche Macan 7DCT / 1993 - Cadillac Allante / 2023 - RAM TRX (on order) |
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03-17-2007, 05:17 PM
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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.
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03-17-2007, 05:19 PM
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Detached Member
Join Date: May 2003
Location: southern California
Posts: 26,964
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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.
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Hugh |
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03-17-2007, 05:19 PM
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Automotive Monomaniac
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Bingo!
 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. 
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2018 - Porsche 911 Carrera 7MT / 2018 - Porsche Macan 7DCT / 1993 - Cadillac Allante / 2023 - RAM TRX (on order) |
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03-17-2007, 05:20 PM
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Join Date: Oct 2004
Posts: 15,612
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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.
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03-17-2007, 05:20 PM
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Automotive Monomaniac
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Quote:
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!
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2018 - Porsche 911 Carrera 7MT / 2018 - Porsche Macan 7DCT / 1993 - Cadillac Allante / 2023 - RAM TRX (on order) |
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03-17-2007, 05:55 PM
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