Trailer wiring harness installation?

Tiny
RBENNETT2
  • MEMBER
  • 2008 TOYOTA TUNDRA
  • 5.7L
  • V8
  • 2WD
  • AUTOMATIC
  • 88,000 MILES
I am trying to replace a 4 pin trailer wiring harness with a new 7 pin. The new harness has 2 connectors, 1 with 5 wires and another with 2 wires (black and blue). The 5 wire end plugs into the existing receptacle but there is nowhere to connect the 2 wire connector. How do I connect it?
Tuesday, August 16th, 2022 AT 12:13 PM

5 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

When you say the wires are blue and black, is that on the new harness? I ask because those could differ based on the manufacturer.

I attached the wiring schematic for the trailer tow circuit for you to reference. I have a question. You have the five-pin connector connected, correct? If so, do you get power for all the lights such as signals, brakes, backup, and parking lights? If so, my guess is that the two-pin connector would be for an electric brake controller. Are you installing one?

Let me know.

Joe

See pics below.
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Tuesday, August 16th, 2022 AT 7:42 PM
Tiny
RBENNETT2
  • MEMBER
  • 3 POSTS
Hi Joe,

Thanks for responding. Yes, I have installed an electric brake controller. I do have the 5 pin connector connected. Everything works but the electric brakes on my travel trailer. I’m assuming because the other 2 wires are not connected to anything, and they are what operate the electric brakes.
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Tuesday, August 16th, 2022 AT 9:07 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

Yep, that sounds like the issue. If you have installed the brake controller, it should have a wiring schematic for installation. It has been a while, but I remember when installing them, I had to run new wiring from front to back from the controller and power.

Does the schematic you got indicate doing that?

Let me know.

Joe
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Tuesday, August 16th, 2022 AT 9:20 PM
Tiny
RBENNETT2
  • MEMBER
  • 3 POSTS
Hi,

The schematic shows 2 connectors on the truck that connect directly to the 2 separate connectors on the wiring harness. I think the Tundra's with the complete tow package are equipped with the second connector. My Tundra doesn’t have the tow package. It does show that the blue wire included in the 2 wire connector controls the trailer brakes.
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Tuesday, August 16th, 2022 AT 9:31 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

I suspect you will need to run new wiring from the controller and power and make a connection to the one you have. If your vehicle didn't come with the trailer tow package, chances are that wiring just doesn't exist on your truck.

When you installed the new brake controller, was there a wiring schematic with it?

Let me know.

Joe
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Wednesday, August 17th, 2022 AT 7:07 PM

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