'99 VW passenger brake light works when head lights off, does not work when head lights on. Why?

yeye2160

The passenger side brake lights on my '99 VW do not work when the head lights are on, but do work when the head lights are off. Replacing the brake light does not fix the problem. Any recommendations?

thecardoc3

Measure the circuit voltage drops under the conditions that the symptom occurs under. If you measure a voltage on the ground above .3v then there is a problem with the ground circuit. If the other voltage inputs are correct and there is no voltage drop on the ground circuit, then you probably have a bad socket.