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Help with stock trailer plug wireing

RevN3

RevN3

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Tacoma3G O.G.
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Location
Eugene, Oregon
2017 TRD OR DCSB Manual
Blazing Blue Pearl
Okay, so I've known for awhile that the left light connection (4 pin plug) works for lights but not brakes nor blinker. It never worked from the factory. I've tested with multiple trailers/testers and it's a repeatable issue. I havn't got around to messing it with it until today though....because I'm borrowing a trailer and going camping this weekend. Nothing like under the gun repairs!

Anyway I had a few questions:

1. There is a fuse labeled Towing Tail in the fusebox. It seems to have nothing to do with the 4 plugs at least. Is that just for the 7 pin connector? I can unplug it and the 4 pin keeps working as well as it was before.

2. I've traced the wiring back from the trailer plug to the first cluster but it doesn't seem to tap into the blinker there. I only found that out after cutting away a LOT of electrical tape. Where the heck do the wires tap in from the trailer plug?

3. I found a plug in the fusebox that when I unplug it the 4 pin seems to go dead. Blinkers on the truck still work though and there are a lot more wires in the bundle than go to the 4 pin. That can't be where the four pin taps in, can it?

It seems like they made this setup needlessly complicated. Every 4 pin I've ever set up has tapped in with arms length of the plug. This has me confused though. Any guidance would be greatly appreciated.
 
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Looks like I have 4 thick wires, blue, green, black and white; as well as three thin wires, light blue, white and purple. Any idea what goes to what?
 
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Well shit, I followed the wires all the way to the fusebox, testing as I went. I now know a lot more about the wiring at the back of my truck. Bad part is...the problem goes all the way to the plug in the fuse box and I don't know where to go next. I'm considering just buying a Curt harness and plugging it in at the rear. This wiring scheme is totally insane. Why would you not tap the trailer blinkers off the tail-lights?
 
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Does the 7-pin plug have the same issue? I haven't looked at the wiring myself. I'd imagine a light issue on the 4-pin would be common with the 7-pin. If the 7-pin is good though, buy a 7-pin to 4-pin adapter so you can take the trailer this weekend without having to fix it right away.
 
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Spock said:
Does the 7-pin plug have the same issue? I haven't looked at the wiring myself. I'd imagine a light issue on the 4-pin would be common with the 7-pin. If the 7-pin is good though, buy a 7-pin to 4-pin adapter so you can take the trailer this weekend without having to fix it right away.
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Yup, they both have the same issue. i was hoping the issue was with the plug itself but I traced it all the way back to the fuse box.
 
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