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Old 08-01-2023, 02:31 PM   #1
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Brand: Thor Motor Coach
Model: Miramar 37.1
State: California
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THOR #12698
7 Pin Trailer harness stopped working

While on the last day or our cross country trip, I hooked up my car to the Blue Ox Tow Bar System. I have the Demco Stay N Play Duo Braking System. The braking system would not activate, the tail lights on the car would not work. I found that the trailer harness lost all power. I looked in the Ford Manual for the fuse thinking it blew. I went under the hood of my 2022 Thor Miramar and swapped out a fuse for the one listed and it still did not work. I also noticed that the newly installed cigarette lighter plug (I had installed at a shop) was also dead. When I got home I checked for the fuse panel under the dash to check for a fuse there with no luck after switching fuses from the Ford manual. I also tried following the wire from the newly installed dash cigarette lighter plug thinking they may have tied into the 7 pin harness and installed an inline fuse but had no luck unless I take the dash a part. I found that my coach has three different size fuses. The regular automotive, the Mini automotive and the micro automotive ones. I only carried the regular size fuses and now have to order a set of the other two in case I have another issue.
I am stumped at this point where else to look to locate the blown fuse(if it is that) for the 7 pin trailer harness.

Paul

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Old 08-01-2023, 03:13 PM   #2
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THOR #7035
I don't have your braking system but looking at the manual it seems it needs a constant 12 VDC to the controller which I assume comes from the TOAD's battery? Have you checked for power to the Demco controller.

In any case this is a job for a multimeter. Do you have one and know how to use it?

Could be as simple as a bad ground.
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Old 08-01-2023, 05:12 PM   #3
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THOR #12698
The 7 pin connector supplies the 12v to the toad's battery to keep it charged. I did check the inline fuse to the Demco System and it was good. For some reason I am not getting power through the 7 pin trailer harness to the 7 pin connector. to the toad I will have to get the multimeter out and start checking.
Thanks
Paul
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Old 08-01-2023, 06:30 PM   #4
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Check the ground wires.
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Old 08-02-2023, 12:02 AM   #5
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Thanks for the suggestion. I will check the ground wires.


Paul
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Old 08-02-2023, 11:12 AM   #6
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Maybe not the problem, but I had a problem on my F150 once. No fuses blown and only a rear tail light not working as the blinker.

I looked up for a do it yourself remedy. Of course: YouTube

There is a code reader that plugs in, not an expensive one either (like $10 range). It worked via bluetooth with an app on the cell phone (free app too). I cleared faults, which was a ground fault, and all was better.

It happened once more, that's when I noticed it was only after using my one trailer. So I looked over the trailer wiring, cleaned up the ground connection to its frame, then never had the problem again.

Sorry I cannot give product's names at this time because the truck is with the wife, and my cell phone screen zilched, meanwhile my new phone is some 10 days out,
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Old 08-02-2023, 01:35 PM   #7
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Thanks Rusty
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Old 08-07-2023, 01:59 AM   #8
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I have done some more researching and found that I have more fuses to check than I originally thought. I started reviewing the manual closer and found that there are more than 2 fuses that control the trailer wire harness. I only checked two fuses in the main fuse box under the hood and one fuse in the fuse box by the steering wheel. Once I figure it out, I will post my findings. Right now my motor home is at the storage facility away from my house.

Paul
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Old 09-26-2023, 02:31 AM   #9
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A little follow up on my 37.1 Miramar 7 pin trailer wire harness. I had it in the shop on other warranty items and had them look into the trailer harness not working. They replaced a 15a fuse in the under the hood fuse box and called it fixed. When I arrived and hooked up my car(flat towing back home), the wire harness only operated the left rear tail/brake lights on my tow vehicle and not the right side. After unhooking it and re-hooking it back up, the left side stopped working. They did not have their electrical guy at the shop(Saturday pick up) so I had to take it home. Once I got home, I discovered that the 15a fuse had once again blown and I also replaced the other 5 related trailer towing harness fuses just to be sure they too were good. Once I did that, I hooked up my tow vehicle and everything was back up and working as usual. I drove my motor home back to our storage facility with my car in tow. When I arrived, I decided to check the lights again and once again they had stopped working again. Now I will start looking at which fuse has blown again and follow it through from the harness connecter in the rear to the front for a possible bad wire or connection/short. I did check the battery grounds in the battery bay and all were tight. I plan on getting a 7 way to RV socket LED tester to start my journey into locating the wire short issue. I have found that I didn't have the correct fuses onboard when it first blew when we were in Tombstone. My coach uses Micro, Mini, Regular and Micro Cartridge style fuses. I also found that there are 7 different fuses used for the trailer wire harness(makes sense since it is a 7 pin harness).

I also had them install a heat shield between the area above the catalytic converter and below the coach floor. The interior floor was getting hot when ever we drove it around. There have been issues reported where the exhaust lines were too close to the Rotocast compartment walls causing them to melt from the exhaust heat. My exhaust is far enough away from the compartment walls.

Paul
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Old 09-26-2023, 02:48 AM   #10
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THOR #1469
Quote:
Originally Posted by paulwadley View Post
A little follow up on my 37.1 Miramar 7 pin trailer wire harness. I had it in the shop on other warranty items and had them look into the trailer harness not working. They replaced a 15a fuse in the under the hood fuse box and called it fixed. When I arrived and hooked up my car(flat towing back home), the wire harness only operated the left rear tail/brake lights on my tow vehicle and not the right side. After unhooking it and re-hooking it back up, the left side stopped working. They did not have their electrical guy at the shop(Saturday pick up) so I had to take it home. Once I got home, I discovered that the 15a fuse had once again blown and I also replaced the other 5 related trailer towing harness fuses just to be sure they too were good. Once I did that, I hooked up my tow vehicle and everything was back up and working as usual. I drove my motor home back to our storage facility with my car in tow. When I arrived, I decided to check the lights again and once again they had stopped working again. Now I will start looking at which fuse has blown again and follow it through from the harness connecter in the rear to the front for a possible bad wire or connection/short. I did check the battery grounds in the battery bay and all were tight. I plan on getting a 7 way to RV socket LED tester to start my journey into locating the wire short issue. I have found that I didn't have the correct fuses onboard when it first blew when we were in Tombstone. My coach uses Micro, Mini, Regular and Micro Cartridge style fuses. I also found that there are 7 different fuses used for the trailer wire harness(makes sense since it is a 7 pin harness).

I also had them install a heat shield between the area above the catalytic converter and below the coach floor. The interior floor was getting hot when ever we drove it around. There have been issues reported where the exhaust lines were too close to the Rotocast compartment walls causing them to melt from the exhaust heat. My exhaust is far enough away from the compartment walls.

Paul
Had the same issue when my WK2 was setup for flat towing. The installation folks did a lousy job on the wiring. Mine kept blowing the right fuse. RoadMaster regional rep came to the house and straightened things out and then went and re- trained their certified installer. Haven’t had a problem since.
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Old 10-07-2023, 09:56 PM   #11
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THOR #12698
A quick follow up on the issue with the 7 pin trailer towing harness problem. I changed out a 15 amp fuse(again) and started looking at a possible ground/loose wire issue. I used my new 7 pin wire harness tester from Curt industries to help isolate the wire issue. While I was changing my engine oil on the coach, I found a very loose ground wire. I tightened it up and tested the 7 pin harness again. Everything started working correctly. I then drove my motor home 14 miles to our storage facility and checked the 7 pin harness again. It was still working correctly. Looks like the issue was the loose ground wire in the engine bay area causing the fuse to blow.

Paul
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