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Troubleshooting Turn Signal and Brake Lights On ZCI 119250KIT Not Working On 2017 Mercedes-Benz C300


I installed this on my Mercedes C300. It has a two wire system tail on its own wire, brake/turn on a separate wire. I can get the tail light to work properly, but not turn/brake. This car has LED tail lights with very small wire. It uses two wires for the tail light Pin 1 and2, so I ran both though the sensor and it works fine. The brake/turn line is on Pin 4, and it does not work. Is it possible that the LEDs dont draw enough current to activate this unit? Or am I doing the training wrong? I did 5 seconds each: Lights, brake, right, left. with a couple of seconds in between. Do I need to do each longer? Or with a longer break in between?


Expert Reply:

There are a few possible causes to why the brake and turn signal functions of the ZCI Circuit Protected Vehicle Wiring Harness # 119250KIT are not working on your 2017 Mercedes Benz C300.

First 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. Using the included circuit tester while the turn signals are on will allow you to confirm the correct wire.

Next if it is still not working double check that the ground wire on the module is securely connected to bare corrosion free metal.

If the issue is still not resolved then pull the fuse from the power wire to the battery and re-do the learning for the module. To do this you will need to reinsert the fuse, and then turn each function of the harness on for at least 5 seconds (Brake lights, turn signals, head lights to activate tail lights).

This harness works with incandescent or LED lights so your vehicle having LED lights will not be an issue.

If the above troubleshooting steps do not fix the issue, just let me know and we can go into more in-depth troubleshooting.

I included a video of the # 119250KIT being installed in a similar Mercedes-Benz for you to take a look at.

expert reply by:
Samuel C

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