2003 gmc yukon denali acc wire special

2003 Yukon Denali with Factory Navigation (non touch screen)

Looking for 12V accessory wire.  Problem, have found regular accessory wires that shuts off when you turn off the key, but I'm looking for a 12V that stays on until you open the door.  On GMC's the radio continues to operate after removing the key until you open the door (or after a number of minutes, maybe 15?).  I'm looking for 12V+ that follows that scheme.  Have wired in a video modulator into the nav screen but using regular accessory 12v it shuts off on key removal even know the radio stays on until door opens.  This results in LOS to nav which causes the screen to go crazy.  If I can find 12v that stays on till door is opened I will have acheieved my goal.

Regards,

Roveer

Based on your suggestion to use a harness this would mean that the voltage is present in the current harness.  I tested for it and the only one I found was the backlight 12V which varied based on the setting of the dimmer wheel on the dashboard.  It varied from 2V to 12V.

I was thinking of using this wire to drive a relay which would switch a constant 12V which would give me what I want.  Does this make sense? I've never worked with relays before, but understand the concept and the wiring diagrams I've seen are pretty straight forward.  If so, does Radio Shack sell anything that I could use or am I talking special order?

Thanks,

Roveer