Why Does 4-way Connector Harness On 2003 Chevrolet Express Van Have Red Wire Grounded?

Question

Question:

Ive been having nightmares over my trailers taillights2018 Coleman. I finally tested my tow vehicle today 03 Chev Express 3500/Roadtrek and think I have found the problem. In the rear drivers post I found the trailer wiring harness and module. What I found confusing is it appears the power and ground wire are crimped together and were bolted to the frame. There is no brand name or model number on the module. Its pretty old. Is there any reason for an installer to crimp these two wires to ground? Am I missing something? Oh by the way if you have a Roadtrek like mine the chances are mice have been getting in your vehicle. The bottom of the rear posts are open and open all the way to the top and into the moulded pieces over the side bedroom windows. I filled the bottom of the post holes with a chunk of charcoal pre-filter from an air cleaner. It still allows moisture and air through and mice wont eat the charcoal material.

asked by: Tim W

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Expert Reply:

Based on the picture you provided it looks like the harness you have was designed for either a 2-wire (combined brake and turn signals) or 3-wire (separate brake and turn signals). Since your 2003 Chevrolet Express Van 3500 has combined wiring you would need to ground the red wire, which is what they have done.

You didn't mention what exact issue you are having regarding the taillights on your 2018 Coleman trailer, but I would start with using a circuit tester like # PTW2993 to test each function of your 4-way connector on your vehicle while a friend applies the brakes, turns on the turn signals, and turns on the head lights one at a time.

Since all of the harness currently offered for your van do not have a module, nor do they have the red wire for separate wiring you may be better of just going ahead and replacing the harness with the # 55540 which is confirmed to fit your van.

If you find that the harness is working fine, just let me know exactly what is not working on the trailer and I would be happy to help you troubleshoot.

I included a video of the # 55540 being installed for you to take a look at.

expert reply by: Samuel C

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Customer Harness
(click to enlarge)

Answer 1

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Answer 2

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Answer 3

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Answer 4

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Answer 5

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Answer 6

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Answer 7

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Answer 8

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Answer 9

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Answer 10

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Answer 11

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Answer 12

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