If this is in the wrong spot or I’ve broken any rules, apologies. The staging area didn’t allow me to post. This only gets into locating the cold-side brake switch power, couldn’t find anything about it online. Long story short, it was the green-white wire coming out of the brake switch behind/below the gauge cluster, pictures below. I’ve got a 1994 4runner.

Disclaimer and longish story: If you’re looking at this and have a 89-95 4Runner like me, you know it wasn’t made to pull much, certainly not anything big enough to have trailer brakes. Don’t pull your yacht behind a 4Runner. Don't pull anything with trailer brakes behind your 4Runner. I usually don't pull anything with the rig, but I've got a trailer and it might have to tow a couple times until the COVID production slowdown is over with and I can get that replacement 2500 Silverado.

A trailer brake controller needs a signal that the driver has pressed the brakes to send signal to the 7 pin on your trailer. Most American trucks have a wire coming off of the brake pedal bracket fairly easily located, accessed and wired in. Unfortunately, on our trucks, the switch and wire harness is pretty deep up in the dash. I guess you could find the cold-side wire somewhere else in the cab along the floor of the cab heading to the back of the truck, but I couldn't find a schematic and instead went this route. It's doable. You need to pull the gauge cluster to see the top of the wire harness. The switch that the harness plugs into is directly behind the steel tube that supports your dash, not exactly easy to get to. The harness lead is really only about 5-6” long, so it’s a tight fit to locate, unplug and then solder in. I hate the plastic tap contraptions that were popular for a while so I instead have some of the low-temp tin/solder shrink connectors that I use on jobs like this.

A wide shot of where this thing is behind the dash - my probe is poking the back end of the harness plug:

1994 4Runner - brake switch location


Below is the dash with my probe lit up after finding the cold side brake wire (brake pressed):

1994 4Runner dash, brake switch harness probe

Below is a picture of the brake switch, this is what your harness plugs into:

1994 4Runner brake switch plug


The rest is standard stuff. Piggy an aux power source. I tapped the gauge light fuse with a piggyback. Powered the 7-pin harness off of the battery. Below is the 7-pin, just a hair away from the spare hold that the bar needs to go into diagonally, it just misses:

7-pin trailer brake