Retained Accessory Power - Rap - Tap Point

hdavid66 · September 15, 2008

Hi All -

Firstly, This article applies to a 2006 GMC Sierra 1500 Pickup. I'm sure it will cross over to other year trucks, but I can't say for sure which years / models. Use the following info at your own risk!

After scratching my head for a while and after doing a lot of reading here on gm-trucks.com; I figured out how to make myself a "RAP Accessory" power wire.

The problem came when I wanted to install my aftermarket Pioneer XM radio / FM Modulator in my truck. I was able to find an accessory power wire quickly, but it really wasn't what I wanted. By using accessory power to power the XM Radio, it would go off when the key was turned OFF, however the OEM radio would stay on using RAP power. The result was I couldn't listen to the last few verses of my favorite songs and after the XM Radio died I got loud static on the OEM Radio (because the FM Modulator kicked out.)

This problem resulted in the quest for the elusive Retained Accessory Power point.

The problem is that, in my vehicle at least, GM turns the radio (and other stuff too) ON while in "RAP Mode" with a command send on a Data Bus from the BCM to the radio. The BCM computer says "Hey You, Radio - Stay on till I tell you to shut off." The BCM computer then monitors the door switches and also starts a counter for 10 minutes. When someone opens the door or the 10 minute timer expires the BCM computer recognizes this and says over the data bus to the radio, "Hey You, Radio - Shut Off Now." Power to the device is not actually toggled off; the BCM commands the radio to shutdown over data bus.

The short part of the story is that a Retained Accessory Power Wire doesn't exist (with one exception).

The exception is a circuit setup to power the sunroof with RAP power. Even if you don't have a sunroof there still should be enough of the wiring to do what you need to do.

There are two places that you can tap this wire one is in the Right Body Fuse Panel and the other is at the BCM.

In the Right Body Fuse Panel,(in the same place as your regular interior fuse panel just on the other side of the dash) is accually a juction block with a bunch of plugs. Your looking for Connector 6, it is in the in the lower right corner of the panel. If you have a sunroof there will be a light green plug in it. It is a six terminal plug. Your looking for the wire in position D. It should be a small dark blue wire.

or

The BCM is under the dash, just to the right of the steering wheel. On Connector 2 on the BCM (24 pin gray connector), pin B3 is RAP supply voltage for the sunroof relay. This is shown as a dark blue wire in schematics.

That dark blue wire is the wire you need. When the truck is RUNNING, ON, ACCESSORY or RAP Mode there is 12 volt power on this wire.

I didn't tap the wire directly; I'm not sure how much power that wire would safely provide. I used the Dark Blue wire here to switch a relay to run the accessories that I wanted to run on RAP power. If you have a sunroof you'll have to wire in a second relay in paralell.

So there you go - you now can make your own Retained accessory power.

As I have time - my goal is to get some pictures up here to help better explain.

Further reference on the forums:

Retained Accessory Power

http://www.gm-trucks.com/forums/index.php?...st&p=414748

Sunroof Curcuit Schematic

http://www.gm-trucks.com/forums/index.php?...st&p=557849

Dave

DofD · September 15, 2008

Good post.

I have this information for the GMT900's

Installation Instructions -

12 Volt Accessory Power Supply

1. Disconnect the battery negative (-) cable at the battery. The

negative (-) battery cable must be disconnected before the

positive wiring lead is connected to the power accessory.

2. Locate the power supply harness under the instrument panel

near the center of the vehicle. The wire bundle consists of six

blunt cut wires, two red/white (battery hot), two black (ground),

one light green (Ign hot) and one light blue (Ign hot).

3. Remove the tape to release the wire bundles from the

power supply harness.

4. The IGN A and IGN B wires have voltage supplied and are

HOT when the ignition is turned to ACC, RUN or RAP

(Retained Accessory Power).

The BAT A and BAT B wires have direct voltage supplied

and are HOT at all times.

The combined electrical load of IGN A and BAT A must not

exceed 21 amps (250 watts). Additionally, the combined

electrical load of IGN B and BAT B must not exceed 21 amps

(250 watts). The combined electrical load of all circuits must not

exceed 42 amps (500 watts).

5. Prepare the wires that are to be used to connect the power

accessory. Do not remove the unused wires. Tape unused wires

back in their original position under the instrument panel.

6. Complete the wiring installation of the customer added

accessory with additional wire required for the specific

electrical accessory power connection. The wire gage,

12 gage (3.0 mm2), should be the same as the wiring of the

installed harness.

7. The ignition must be turned to OFF or ACC prior to attaching the

cables to the battery, or serious damage to the Vehicle Control

Module (VCM) may result.

The windshield wiper switch and the radio must be turned off

before attaching cables to the battery.

8. Reconnect the battery negative (-) cable to the battery. Torque

the bolt to 3.7 lb-ft. (5 N•m).

9. Reset the clock time and radio pushbuttons as desired.

ap0352 · March 24, 2010

I've been searching for a RAP signal to power my DVD player and followed this tutorial today without much luck....

I found the blue wire on the right side of the dash that was mentioned in the first post. I pulled out the meter and tested the wire and did not get a 12+ acc. signal. In fact I got a low voltage, 4 volts reading. I tried tapping into it anyway and it would not power on my dvd player....

I then decided to look for the bundle of wires mentioned in the second post since I do have a GMT900 but I can't seem to find the bundle. I did find a bundle of wires with other colors. I think it was 6 wires with brown, blue and a few other colors that was taped up right next to the fuse box thing...

Anyone know where this bundle actually is? Anyone found RAP power in the right side dash panel of the GMT900's?