Join Date: Jul 2004
Location: Tacoma, WA
My Ride: '84 Dodge Rampage
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How-to: Radio turnoff delay circuit
Ok. First I'll start with the reason you might want this circuit. Most modern American cars have a radio delayed turnoff feature. What it does is it keeps the radio on after you turn the car off. The radio stays on until the driver's door is opened. It's amazing how quickly you can come to expect this feature to be in all cars. It's also remarkably easy to add to any car, I have added it to at least 6 or 7 of my cars and past cars. The only cars I could see having a problem with this circuit would be positive door triggered cars, such as Ford's. But it's a small revision to get it to work with even them.
Anyways, let's go into an explanation of how this circuit works. Using two standard readily available Bosch style relays, once the ignition is turned on, one relay is put into a self-sustaining power loop, the other relay is just there to break the loop. A diode on the incoming accessory wire from the car keeps the power from backfeeding into the rest of the car (this would blow the accessory fuse, don't get any ideas). The accessory circuit also feeds the radio, so that opening the door with the car running does not kill the radio.
I appologize for the crudeness of my schematic, I'm far from being an artist. The funny looking loop of wire near the incoming constant 12v source wire is to let you know that those two wires are not connected. If you look at the bottom of a Bosch relay, the terminals should look the same and have the same numbering. You have to use SPDT relays, SPST relays commonly used for foglights will not work.
This circuit will work with the stock radio, I have it setup that way in my turbo Horizon. But I recommend doing it with an aftermarket deck and harness adapter, it's easier if your not chopping into the factory wires and trying to figure out which is constant and which is switched.
As for getting ONLY the drivers door, not the passenger door(s), you'll need to pull the kickpanel on the driver's side, pull the door pin, and find the wire coming off of it going to the dome light. (It's yellow on our TD's) Find the wire in an easily accessible place, and cut it. This will kill your dome light. Worry not. You need a 3amp or larger diode, Radio Shack or some other electronics store will have them. You want to put the diode in that wire where you just cut it, the diode will have a white stripe on one end, you want that stripe on the doorpin side of that wire. You also want the wire going to your radio circuit on that side of the diode. Hook the other side of the diode to the dome light side of the yellow wire you cut originally. This will keep your dome light working, and keep your passenger getting out from killing your radio. :)
I assume there will be many questions, feel free to PM me. Please leave me some positive feedback if you find this helpful. :)
Last edited by onerippinturbo2; 09-11-2013 at 09:08 PM.