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View Full Version : DIY - Make an ignition controlled aux power supply


sura
02-19-2009, 08:18 AM
For E65/E66:

I got tired of using the aux power cigarette lighter outlet in the passenger footwell for my satellite radio. Waiting for the car to enter sleep mode would sometimes take 15 minutes, sometimes 2 hours. I didn't like the more than .50 amp draw while the car was off.

After searching everywhere I finally found concise instructions, so I can't take credit for tihs. Problem is, I now can't find the source to give proper credit.

Anyway here it is:

Supplies needed:

A SPST 12v relay. I used one I had from Radio Shack http://www.radioshack.com/product/index.jsp?productId=3020762

Some wire & spade connectors.

Procedure:

1. Remove the driver's under-dash panel.

2. Locate the brake light switch and find the green/black wire. This wire is used to trigger the relay. This wire will have +12v with ignition on; 0v with ignition off.

3. Locate the large red 12 ga. wire to the left of the brake light switch. This is in a bundle to the upper left corner. You will tap into this wire for your power supply.

4. The rest is up to you. I ran my wires over to the center console and stuffed the relay and connections back behind the heater box, behind some gray foam in there.

Here's a simple diagram:

http://www.perfectmarketaudio.com/relay.jpg

Sean172
02-21-2009, 12:14 PM
HI, I liked your post, I want to do just what you did. I want to find a new power source for my sattelite radio. Why did you use a relay. I am not a mechanic but I was planning on dismantling the cigarette lighter plug that came with the radio, as it reduces the power to 5.2 v 1.5A, repack it and just tap into another 12v supply somewhere hidden. Is this feasible? Thanks,
Sean:dunno:

sura
02-22-2009, 02:05 PM
dismantling the cigarette lighter plug that came with the radio, as it reduces the power to 5.2 v 1.5A, repack it and just tap into another 12v supply somewhere hidden
Yes, this is what I did. Originally, I used the satellite radio's power supply and tapped into the aux power cigarette plug wiring behind the plug. This is not a true ignition controlled source as it relies on the car's power monitoring system (whatever that's called) to turn it off when the car goes into sleep mode. I wasn't happy with that.

Why did you use a relay
I used a relay to completely isolate the draw from that tiny brake switch wire. With the complex wiring in these cars, who knows what would happen if it sensed a larger than normal current draw in the braking system? That was my thinking. Current draw through the relay coil has to be minute. The relay is cheap and made me feel safer in messing with the wiring.