1990 K3500 brake controller and plug wiring setup

[William Keiter]

Can anyone tell me a good trailer wiring set-up from adding a 7-way plug and wiring all the way to adding a brake controller. I have a 1990 3500 with a receiver and no wiring whatsoever. Guessing previous owner removed.
Have been trying to research a good set up but figured I best ask for opinions on what seems to be best before diving in. Thanks

 

[Nad_Yvalhosert]

Look under your brake booster. There should be a coiled up 2 wire set: blue and orange. That'll be the 12V battery wire, and the trailer brake. Trace them to the back.
Then you can buy a 4 pin, T-shaped 4 flat adaptor. Easiest thing is to cut off the 4 flat connector, throw in the blue & orange, and a wire to reverse (center pin on the 7-wire).
Be sure to zip tie the wires to keep them from abrasion, and grind a fresh spot on the frame for the ground wire.

 

[BNielsen]

Your truck being a 90 it should have the existing "tow package" wiring already run and already tucked up; I had some janky wiring done by one of the POs, and I wasn't full confident in it so I bought this kit from E-trailer,
Trailer Brake wiring

 

[Supercharged111]

It may or may not have that wiring being a 90. If not, you'll need to run an orange wire for 12V constant and a blue wire for the trailer brakes, or use whatever colors you want. You'll need to fuse the 12V wire yourself as there is no convenient fuse box waiting for you to pull off of. You'll ground the 7 way plug to the frame, and the other 2 are nice and easy to tap into.

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You can buy a 7 pin that has a plug to accept that or chop it off and wire it direct to the plug.

 

[William Keiter]

It may or may not have that wiring being a 90. If not, you'll need to run an orange wire for 12V constant and a blue wire for the trailer brakes, or use whatever colors you want. You'll need to fuse the 12V wire yourself as there is no convenient fuse box waiting for you to pull off of. You'll ground the 7 way plug to the frame, and the other 2 are nice and easy to tap into.

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You can buy a 7 pin that has a plug to accept that or chop it off and wire it direct to the plug.

Looking under the hydroboost for the wiring it appears I have six wires going to the rear, can’t see if I have an orange or blue and will have to clean them off a bit and trace them back. If I recall the brake and turn signals take about 4 wires.

 

[Supercharged111]

Looking under the hydroboost for the wiring it appears I have six wires going to the rear, can’t see if I have an orange or blue and will have to clean them off a bit and trace them back. If I recall the brake and turn signals take about 4 wires.

The plug in deal I linked is those 4 wires, so the rest are ground, 12V, and brakes. If you had the wiring, it wouldn't be on a plug. It'd be 2 extra wires, unterminated at either end.

 

[GMCTruck]

There is a wire loom that runs along the driver's side frame rail to the back of the truck. You can open up the loom at the back and look for the orange and blue wires there to confirm they are present. The orange wire is 10 gauge and the blue is 12 gauge. There may be another trailer wiring loom containing the brake light and turn signal wires tucked up along the back crossmember.