Where to tap for power?

msheldon · Jul 24, 2004

I'm installing an LCD head for a rear-view camera system, and need a good place to tap for power in the cab. In this case, It should be powered with the key turned (accessory or engine running), since this camera serves as my rear-view mirror while towing. I've found a couple places to tap that are powered all the time, and one on the brake controller harness that is powered when the lights are on, but not one for ignition yet...

whitethunder · Jul 24, 2004

I'm not 100% sure but you have 2 12 volt receptacles in the dash 1 is for the lighter one works with the truck off the other only when the ignition is turned on!

That's where I would start you may want to check with Dichris he is Mr Capacitor!!

good Luck

02-Z66 · Jul 24, 2004

use a wire off the radio harness for power. you a "switched" 12 volt power source wire on that harness. i am guessing you may mount the monitor in the vicinity of the radio, yes? if not, you could still use this location.

my info is a little foggy, but terminal positions 9 and 10 on the radio, counting from right to left starting at the bottom roght, are your IGN 12 VDC IN and BATT 12 VDC IN respectively. so when you pull the harness number one will be on your bottom left as you look at it. not sure which radio you have, but i think this holds true no matter what. to be sure i would just probe the pins with a test light. if you power it will light. cjeck with ignition off. the pins that lights in the harness with no ignition power obviously is the one you don't want.

msheldon · Jul 24, 2004

Well, both of the 12v power plugs are on all the time, so I can't use them.

I was kind of hoping for something easier to get at than the radio harness, but I guess that's my best bet. I've got the video head mounted in front of the empty cubby underneath it.

02-Z66 · Jul 24, 2004

if you can't mount it near the console you can still tap into the radio harness wire, and then run the wire throught the dash to the left. then take it up through the pillar to the visor if you plan to mount there.

carndt · Jul 24, 2004

The Snakeeyes "always on" option (on with key lke you want) on my 03 1500 uses a fuse tap in the driver's door fuse panel.

It's the second from the "left top" as you face that fuse panel, 10 amp (red) marked SEO ACCY.

msheldon · Jul 29, 2004

carndt said:
The Snakeeyes "always on" option (on with key lke you want) on my 03 1500 uses a fuse tap in the driver's door fuse panel.

It's the second from the "left top" as you face that fuse panel, 10 amp (red) marked SEO ACCY.

Just did it, perfect.

I wasn't familiar with the fuse taps, then had the devil of a time finding anyone who carries them. (Pep Boys)

Thanks!

carndt · Jul 30, 2004

You are entirely welcome...

roygbiv · Aug 19, 2004

The correct way to tap in for ign/acc 12v with RAP circuits is to use the dark blue wire on the BCM under the steering column. You will also need a regular 4 or 5 pin relay. Take pin 87 with a 15 amp fuse in-line and run it to The solid red wire at the ignition switch. Pin 85 to ground. Pin 30 will be your 12 volts output to your accesory. Now this is the tricky part at the BCM under the steering column the second plug in from the left look carefully on the top row of wire the third one in from the left is a dark blue wire this is the RAP wire tap into this wire and put a 1K resistor in-line and run it to pin 86 on the relay and you done. By using the RAP wire with the relay your accessory will work like the factory accessory were when you shut the ignition off the accessory will stay on till you open the door.

sperry · Aug 19, 2004

Remember to dampen the relay coil with a resistor. Relay coils can generate a high voltage spike when they de-energize. A diode can also be used but can damage a source if they short. The resistor (around 1K Ohm) would draw about 1.2 mA @ 12v but becomes a considerable load to a high voltage "spike". I don't know what value resistor GM uses on their relay coils.

(Don't load the BCM directly; thats why the relay.)

Here's a way to tap RAP. GM does it for the sunroof-equipped Av's. (03-04)

(The image is expandable)

roygbiv · Aug 19, 2004

Your correct when you use a cheap relay there is no internal protection on the relay and the use of a 1k or diode on the blue wire is a good idea. If you use a Bosch or Potter&Brumfeild relay they have an internal resistor for protection but those cheap relays that are made in china won't. In any case your right your better off putting a diode or 1k res on the blue wire anyway. I'll change my description.

Thanks
Roy