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Driver Rear Running Light Out

700 Views 6 Replies 4 Participants Last post by  pbethel
Having trouble identifying why my driver side rear running light is not working. This is the top light in the light assembly. My van is a 2021 148 MR Crew van. I have taken off the assembly and swapped the bulb from the passenger side and the light still did not work. When swapping the bulbs, the non working driver side bulb worked just fine in the passenger assembly. I even swapped the assemblies all together and the driver assembly worked fine when connected to the passenger assembly. At this point, I believe I have identified that it is neither the bulb nor the assembly.

The only work I have done to the van recently is messing with the High Specification Vehicle Interface Connector (harness) and C33-H harness to enable my up fitter switches. I have only unplugged and plugged in those harness, I have not connected anything. Also, when I completely remove those harnesses, the rear lights work the exact same. So I don't believe those harnesses are messing with anything.

I have gone through the BEMM and Manual and haven't identified a fuse that only pertains to the driver rear running light. It would appear that other lights would also not be working if it were a fuse.

This happened once last summer but turning off the van and restarting it resolved the issue. That is not fixing anything this time around.

It did rain last night... hopefully it isn't water related.

What am I missing? Any ideas? Local dealer doesn't have a service appointment for 2 weeks...sigh.
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Anybody have experience with this issue or have any ideas?
I recall people in the past with this problem but those were most likely on early model transits, I do not remember the outcome.
not sure if this applies, but i noticed that when i had the receiver and other things in the dash apart/disconnected, the drivers side front and rear lights wouldnt come on when locking the van. i had the trailer brake module, the head unit for the stereo, etc. all disconnected. i am guessing one of the harnesses also feeds power down the side of the van and to the lights. once i plugged in the harness i was adding, everything worked. since the trailer brake controller harness is right there by the plug for the upfitter switches, i would check that first
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Check the ground connections in the rear of the van?
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Thank you for the suggestions.

I will check out the other harnesses in the area and ensure they are all plugged in properly.

As for the ground, I had been installing my subfloor and was trying to wiggle in the plywood a couple of times, I suppose I could have knocked one of the grounds loose. But I have the stock black walls on the lower half of my crew van and I believe that they cover/protect the grounding locations. Ill take a peek though.
Not an original thought.
I watch South Main Auto Repair on you tube. Loose or bad grounds are commonly the cause of unusual lighting problems. Most commonly with Chrysler/Stellantis products though.
good luck
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