OK! I'll give you suggestions, ideas and a couple of photos.

I had my dash apart for a bunch of projects (2021 TRD Off Road (Premium)), and I installed my Redarc Tow Pro Elite at the same time.

Summary:

I installed my controller on the brake-pedal bracket. I spliced together the Tekonsha 3401P harness and Redarc's pigtail-harness. I opted to mount the tiny gain-adjustment dial in the recessed switch area by the driver's right-knee.


Mounting Details:

• Remove Battery (or at least disconnect it).
• Remove lower dash. Mostly it pulls/un-snaps, but there are two 10mm bolts along the bottom.
• I waited many days after battery-disconnect, then also removed the knee-airbag. There are 4x 10mm bolts; I left the wire connected and placed the 'bag + bracket carefully out of the way, while still attached.
• I test-positioned the Redarc controller, then carefully drilled two holes in the pedal-mounting bracket. Make sure everything is clear!!! Spend a lot of quality-time on your back, with a flashlight, and feel around as you move the brake-pedal a bit.
• For certainty of clearance, and ease of assembly, I inserted two 8-32 stainless bolts from the firewall-side of my drilled holes, then I could apply Loctite Blue, lockwasher and nut quite easily from the accessible-side.
• I used double-sided 3M super-sticky-tape and a lower tie-wrap to keep the controller body secure.

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Wiring Details:

• I spliced the Tekonsha 3401P harness to the Redarc pigtail-harness. This goes nicely, because it's color-to-color.
• Stagger/offset the four wire joints, to minimize the "dog knot" in your harness.
• For each splice, I used a Western Union connection, soldered each splice, and slid heat-shrink tubing over each
• I like the ground-lug that Tekonsha adds to the white (ground) wire, and so I re-included that. Just above my Redarc mounting location, there are a couple of factory M6 holes - I applied nickel-antiseize (to ensure a reliable, long-lasting connection) and used a stainless bolt to secure the ground wire.
• I slid larger heat-shrink tubing over all the connections
• I had pushed back/compressed the Tekonsha protective-braid during my splicing, and afterward I slid this all the way up and along my new, custom harness. Looks factory!

The Tekonsha harness + Redarc pigtail are generously long. I easily routed this custom harness, under-dash, toward the driver, well away from the parking-brake, then looped it back in to the controller.

My custom harness is shown in the second photo, looping up at the left, arcing across and over Toyota connectors, then turning down and tie-wrapped to existing harnesses before making it's way to the controller.

Likewise, the Redarc harness for the control-knob is generous, and can be safely routed away from everything.

My approach IS NOT for the impatient! But if you take pride in your work, and want your 4Runner to give you decades of troublefree service, then maybe you'll find something helpful in the way I did this.

Attached Images