Troubleshooting Tekonsha 119251 Running Lights Go Out When Brakes Are Applied

Updated 11/05/2025 | Published 10/30/2025

Question:

I just installed a Tekonsha LCI 119251 in a 1999 Lexus RX300, to tow a 2024 EZ-Loader 67BT 1200. All of the trailer lights will function, but the trailer tail running lights go out as soon as the brakes are applied. They wont go back on unless I turn the headlights off and back on again. Ive already re-attempted the LCI learn mode with no change. Any help would be *greatly* appreciated. Thank you!

asked by: David

Expert Reply:

Hello David, thanks for reaching out. There are a few things you will want to check here. The first will be to make sure the module has a good ground. You may need to sand the ground area to get rid of any paint or corrosion that could be causing a bad connection. It wouldn't hurt to check the ground on your trailer side too, just to rule that out as a possible cause. Also make sure that the driver and passenger side connectors are installed to the correct wire and that the arrow on the connector is pointing towards the light. Sometimes there can be more than one wire carrying the taillight signal.

I have also heard of this issue happening when the module box is overloaded. This happens when there are too many lights pulling too much power on the trailer and the module stops sending power to one function. You could try using a 4-flat tester to narrow this down.

There is also a chance the module is bad and you can check this with a wire tester. If the input signal going into the converter is good, but the output is not correct, the module is bad.

Check all this and let me know your findings. I am happy to continue to help troubleshoot if needed.

expert reply by: Jesse M