Installed Tekonsha T-One And Now My 2005 Toyota Tacoma Won't Shift Out Of Park

Updated 03/13/2026 | Published 03/08/2026

Question:

I installed a Tenkonsha t one wiring harness for a 2005 Toyota Tacoma and now my truck won’t shift out of park.

asked by: Cristian P

Expert Reply:

Hello Christian, thanks for reaching out, and sorry to hear this is happening. If it won’t shift out of park after installing the T-One, the first thing I’d check is your brake lights. On that Tacoma, the truck has to see the brake pedal signal to release the shifter. If the brake lights aren’t coming on, you likely popped the STOP fuse during the install or have an issue with the harness connection.

First I’d unplug the T-One completely and plug the factory connectors back together to see if the problem goes away. If it does, the issue is in the trailer harness, ground, or power lead. Make sure the white ground wire is on clean bare metal and that nothing got pinched behind the tail lights. If that doesn't solve the problem, check that fuse.

Try that out and let me know how it goes. I'm happy to help troubleshoot further if needed.

expert reply by: Jesse M

T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector
(click to enlarge)

Leslie H.

3/12/2026

I started my installation but had to let a shop finish it. Just a little too old. A couple weeks after the installation my Tacoma got stuck in Park, too. Took it to a shop where they found that a “relay pack” had gone bad. Since I had waited to install the hitch, I had no recourse for recovery. So now I have a hitch with no hope of getting it right. Good luck.

Jesse M.

3/12/2026

@LeslieH Hey Leslie, thanks so much for sharing! That's super helpful real-world feedback!

Leslie H.

3/12/2026

@Jessem Hi Jesse? Any recommendations on how to solve my problem? How about a real world solution?

Jesse M.

3/13/2026

@LeslieH Well if the shop said you have a bad relay I'd start there. Otherwise check harness ground and stop fuse. It should be one of those.

John S.

3/12/2026

I second the ground check- It is amazing and weird what a sketchy ground will do... I re did my ground, grinding to bare metal, sanding the lead, etc, and all the strange things; ( one side turn signal worked, and the other did not, etc...) ta da , all was well...!

Jesse M.

3/13/2026

@JohnS Hey John, thanks for sharing. Yea a bad ground can cause all kinds of weird electrical problems. That's always a go-to step for wiring harnesses troubleshooting. Appreciate you sharing your experience!