Sidemarkers come on with brake pedal

[Finchr]

Hi guys. I noticed my passenger side marker is very dimly lighting up when I press the brake pedal. I am guessing is getting feedback from an insufficient ground at the tail light.

I bought new 3157 bulbs but no change, even flipped them 180deg. I swapped the bulb adapters on the harnesses and no change. If I remove the passenger bulb it stops. I t-tapped the ground tail light ground wire near the bulb adapter and ran a 2nd wire to the chassis ground as a test - no change. I removed and cleaned all the chassis grounds - no change. I don’t see any pinched or corroded wires on the tail lights or headlights.

Cleaned and checked the trailer plug too.

Any ideas what to check next? I am now driving around with my parking lights on so I don’t have the dimly lit bulb when braking.

 

[Finchr]

I know no one replied, but in case this comes up in someone’s search, I replaced the tail light bulb holder with my old OEM one, and my problem went away. I have aftermarket halogen tail lights that came with new connectors. When I switched the aftermarket connectors between the lights, it did not make a difference. When I went back to OEM just one the one side, my problem went away.

 

[pacofortacos]

Good find!