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Premium Member
11,253 Posts
Discussion Starter · #1 ·
Hi Guys,

Like it says, I have a 2K model that's undergoing some "modifications"...part of it includes new taillights and some other stuff. I figured while I'm at it, I'd go through the wiring harness and see what's in there, and set up the towing harness again.

Many years ago, the truck had the towing TSB done...small box in the left taillight housing. A couple years ago, I had an odd problem where hitting the left turn signal would cause the reverse lights to flash, and some other garbage in the lighting. Ditching the box solved the problem.

The original 4-pin connector is long gone...eaten by rocks. It also looks like there's more wiring on the harness than the 4-pin could accommodate, anyway.

I'd like to run left/right signal, brakes, reverse, running lights, and power/ground. I assume this is the standard 7-pin connector I keep seeing mentioned.

Here's what I've found on the OEM harness...this is the one under the driver's side seat, by the way, traced to the back of the truck...

Black connector appears to have an additional turn signal line (pin 3 and 5), and additional stop line (pin 7)...these all lead to the connector which was originally linked to the box in the left taillight socket. Pin 11 is common GND for everything on the back of the truck. Pins 10 and 12 are not wired.

On the white connector, there is a black wire at pin 1, heavier gauge than the rest, leading to the tow harness connector. Pin 2 is common hot for running lights (right and left 2-circuit stop lamps, same to towing harness, and license plate lights). Pin 7 appears to be a reverse lamp line leading to the towing harness...I'm basing that guess on the color of the line, process of elimination, and comparison to the lines on black connector which are red (I forget if there was a tracer) and run to the reverse lamps on the truck. The rest of the connector is ABS and fuel related.

I haven't yet tested for hot function on those leads...probably tomorrow. Wiring harness is sitting on the hood right now, covered in masking tape with notes on it :D.


What is the large black wire on the white connector, pin 1, leading to the towing harness connector? I haven't checked it yet...and I can probably answer my own question tomorrow...and my guess is 12V power...but does anyone know OTOH?

What was in that box in the left taillight socket? I have mine somewhere...but it's busted, maybe. Might be possible to fix, but I don't know what was in there in the first place...isolator? Fuse? Relay? Filter? I do have the part numbers...or rather, I can search them out again :cool:. What I'm not certain of is why that box was necessary or if it was the best solution, so I'm curious if you guys have any knowledge or opinions on the subject (um...other than the "just get the OEM part" opinion ;)).

Is there a high-quality 7-pin connector that you guys would recommend? (...Or say "Google search, jackass" :D)

Would you recommend adding a brake controller at this point? Is it a separate connector from the 7-pin?

Note I'm pretty far from plug & play at this point, and I'm starting from the chassis wiring doesn't get more "square one" than that unless I start all the way back at the fuse box :D...

Anyway, going to the OEM connector that originally led to the towing harness stuff, I appear to have stop, L/R signal, running, reverse, GND and 12V power...what do I need to do, to set up 7-pin functionality...just grab a replacement for the old & busted OEM parts?

Here's where I'm at, right now :D...

Note none of this is covered in that paperweight sitting near the front of the hood :rolleyes:..."Body Electrical" is more like "Inside The Cab Electrical"...

Thanks guys,

293 Posts
I can't help with the tundra specific stuff but I can help with the generic stuff. The standard 7 pin:

  • +12VDC keyed (this is likely the larger gauge one you mentioned. It is usually used in travel trailers to charge the batteries, also useful for running some accessories in enclosed trailers)
    brake controller wire
    running lights
    reverse lights
    left turn/brake
    right turn/brake

I am installing one of these on my truck and it seems to be well made but I have not used it yet so I can't say too much about its reliability.

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