Hello everybody a newbie here. I need some help please. I am trying to hardwire fm modulator ( Alpine DPR - RDS1) to my stereo in my Pontiac Grand Prix (2004). Manual for the modulator tells me to connect yellow wire to +12V Power (I can do that just by splicing into red wire going to the radio), ground wire to of course ground (or to black wire) on the radio. But it also tells me to connect REM wire to switched power. When I look at wiring for my 2004 Grand Prix it tells me "Car Radio Accessory Switched 12v+ Wire: The radio harness does not provide a switched power source"
find one in the fuse box instead, then. use a DMM (multimeter) to find a switched power fuse connection, and you can splice into the line there. also, try to ground the unit directly to bare metal, not the black wire in the car's harness, as that wire tends to be about 15-30 feet long, and a very poor ground source. a short, direct chassis ground is superior, and make sure you know what each wire really is in the car harness, don't rely on colors unless you know the color codes for that car specifically. car makers don't tend to use conventional color codes for wiring harnesses the way aftermarket car stereo companies do.
You can have an aftermarket head unit for the price of that modulator, it doesn't make sense unless you love the stock looks (hope that's the case).
Anyways, the ignition switch line is what you are looking for, here is a wiring diagram for your vehicle:
2004 Pontiac Grand Prix Car Stereo Wiring Diagram
Car Radio Battery Constant 12v+ Wire: Orange Car Radio Accessory Switched 12v+ Wire: The radio harness does not provide a switched power source. Run a wire to the fusebox or ignition switch harness for switched power. Car Radio Ground Wire: Black/White Car Radio Illumination Wire: Violet Car Stereo Dimmer Wire: Violet Car Stereo Antenna Trigger Wire: N/A Car Stereo Amp Trigger Wire: N/A Car Stereo Amplifier Location: Located under the center of the rear deck. Car Audio Front Speakers Size: N/A Car Audio Front Speakers Location: N/A Left Front Speaker Positive Wire (+): Tan Left Front Speaker Negative Wire (-): Gray Right Front Speaker Positive Wire (+): Light Green Right Front Speaker Negative Wire (-): Dark Green Car Audio Rear Speakers Size: N/A Car Audio Rear Speakers Location: N/A Left Rear Speaker Positive Wire (+): Brown Left Rear Speaker Negative Wire (-): Yellow Right Rear Speaker Positive Wire (+): Dark Blue Right Rear Speaker Negative Wire (-): Light Blue
