Troubleshooting Tekonsha T-One Trailer Harness Not Working on 2012 GMC Acadia

Updated 07/17/2019 | Published 07/15/2019

Question:

I have a 2012 GMC Acadia on which I installed the Curt C55384 T Connector. Installation took less than 30 minutes. Went to test with the 30512 4 pole flat test connector purchased with the harness and got nothing. Checked for dirty/bent pins and all was good. Research revealed that despite the vehicle appearing to have a factory tow package, it does not have the V92 fuse box under the hood to actually enable the trailer lighting even though all the fuses are there, in place, and tested fine. So instead of ordering a $150 V92 fuse box, I ordered the T One 118451 harness instead. Installation took 30 minutes less really - spent 10 minutes looking for the 4 pole connector tester. Noticed the ground wire was not white as the instructions described but there was a darker wire with the appropriate ring connector and the harness in the box looks different than the one pictured on the box but matched the installation video. Scraped paint to bare metal, connected ring connector to ground, tested, and no lights. Connected the ground straight to the negative battery terminal thinking a ground issue still nada. Connected a 9 V household batter to the tester. Can get LEDs to light one at a time noticed the larger pin needs to be on the + terminal - thought it was negative. Taillights on vehicle work, turn signals work, brake lights work, just not at the 4 pole connector. Any suggestions? It must be something common to both harnesses at this point. At least this gave me an an opportunity to finally replace a cracked passenger taillight cover but would love to get the harnessses working. Suggestions/help?

asked by: Michael B

Expert Reply:

The Tekonsha T-One Wiring Harness # 118451 that you ended up installing is the correct harness for your 2012 GMC Acadia and it will work whether or not you have the tow package so you made the right choice there.

If you happen to have your trailer on hand, the first thing I recommend doing is simply hooking it up to the Acadia and plugging in your connectors. Sometimes those LED testers can be a little finicky so it's possible that the harness works perfectly and the tail lights on the trailer will power just fine in correspondence with the vehicle.

If you aren't able to do this or it didn't work, then I recommend checking the connection points behind the tail lights just to be sure they are fully seated with the factory ports and there aren't any bent pins.

The issue with this particular harness and the Curt model you tried originally actually don't sound like they are related, as the Curt harness didn't work simply because the vehicle isn't equipped with the proper tow package fuses. The Tekonsha harness should work regardless of their presence as its using the vehicle's tail light circuits and is unrelated to any tow package wiring.

Please let me know what you find if you still aren't able to get the trailer lights working and we can continue to troubleshoot.

expert reply by: Chris R