Car Stereos: Power Relay In Harness, stock radio, factory radio

Question
My wife has a 2002 Chevrolet Venture minivan. I replace the radio with an aftermarket radio and purchased a schose wiring harness but there was no power. One of the guys at best buy said I have to buy the exspensive one with the relay in it. Can I take the relay out of the old radio and make it work for this one??

Answer
Hi Jamie,

The issue isn't really as simple as a relay; the problem is that the factory radio is activated with a digital signal from the vehicle's data bus system, instead of a key-switched power wire.  The new head unit needs a switched power wire, but there isn't one in the factory radio plug.

Do you know the model number of the Scosche harness you're using?  

The expensive adapter can read the signal from the vehicle's data bus, and use it to activate a switched power output for the new radio.  It can also generate vehicle warning chimes if they'd otherwise be lost with the factory radio.  If you plug the stock radio back in, then turn the key to the ACC position with the driver's door open, you should hear a chime.  Can you tell if it's coming from the driver's door speaker, or elsewhere in the vehicle?  If it comes from the driver's door, then you'll lose all audible warning chimes when you remove the stock radio, unless you use an adapter module.  If it's coming from under the dash, then removing the radio won't affect the chimes, and all you need to worry about is a switched power source.

If the warning chimes aren't an issue, then you can use a standard wire harness, and just run the red accessory power wire to a key-switched power source.  In the Venture, the easiest option might be to run to the key switch harness under the steering column; the accessory power output is a thick brown wire.  You can tap the new head unit's accessory power wire here, but it's a good idea to put a fuse on your new wire, so that a short doesn't affect your vehicle's ignition circuit.

If the warning chimes would be lost with the radio, then it's probably a better idea to use the adapter module, for safety reasons.

Hope this helps!

Brian