Rear dome light gremlins.
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Rock Crawling
Joined: May 2012
Posts: 350
Likes: 4
From: South Jersey
Rear dome light gremlins.
My rear gate and back seat dome light have constant power going to them regardless of key or door position. I had to remove the bulbs and bought it like this. The front overhead turns off/on as well as dims off as it should. Fuses are good and I have no other electrical issues. (knock on wood) Any advice? I searched quite a bit and have yet to come across a similar issue. 
Super Moderator
Joined: Jan 2011
Posts: 16,322
Likes: 88
From: Savannah Georgia
See page 501 of electrical manual. The circuits you describe have constant 12 volts direct from fuse 6 of subpanel 2. The MFU (multifunction unit) on the back of the fuse panel controls the ground, and it could easily be bad.
Super Moderator
Joined: Jan 2011
Posts: 16,322
Likes: 88
From: Savannah Georgia
The MFU is a timer that is used for all sorts of things, including the 8 minute time out of lights when door left open. If bad it can make lights stay on all the time, or never come on in the first place. Here is the diagnostic for that module.
7. The MFU will then exit the diagnostic mode.
The MFU monitors the door contacts, they don't hook directly to the lamps.
Diagnostic Procedure
1. Close all doors and the tailgate.
NOTE: If the oil pressure switch goes open circuit
(engine is started) during the following procedure,
the MFU will exit the diagnostic mode immediately.
(engine is started) during the following procedure,
the MFU will exit the diagnostic mode immediately.
2. Press and hold the heated rear screen switch
and switch on the ignition.
3. Release the heated rear screen switch within 2
seconds and the MFU will beep to indicate that it’s in
diagnostic mode 1.
4. Press the heated rear screen switch; the MFU
will beep twice. In turn, operate each of the following
switches, heated front screen, rear fog guard lamps,
side lights, headlights, front wiper and rear wiper.
The MFU will beep twice each time a switch is operated.
5. Pressing the heated rear screen again will cause
the MFU to enter diagnostic mode 2.
6. The MFU will provide outputs to the following in
order given below:
and switch on the ignition.
3. Release the heated rear screen switch within 2
seconds and the MFU will beep to indicate that it’s in
diagnostic mode 1.
4. Press the heated rear screen switch; the MFU
will beep twice. In turn, operate each of the following
switches, heated front screen, rear fog guard lamps,
side lights, headlights, front wiper and rear wiper.
The MFU will beep twice each time a switch is operated.
5. Pressing the heated rear screen again will cause
the MFU to enter diagnostic mode 2.
6. The MFU will provide outputs to the following in
order given below:
Heated rear screen relay energised for 2 seconds
Heated front screen energised for 2 seconds
Courtesy lights energised for 2 seconds
Dim dip relay energised for 2 seconds
Rear fog guard lamp energised for 2 seconds
Headlamp power wash energised for half a second
Front wiper energised for half a second
Rear wipe/wash energised for half a second
7. The MFU will then exit the diagnostic mode.
The MFU monitors the door contacts, they don't hook directly to the lamps.
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