My high level brake light has stopped working but it's a bit weird. I removed the light unit and I can measure 11v (close enough to 12v, I presume) at the connector when the brake pedal is pressed. If I apply 12v from a power supply, the unit lights up. When the unit is connected to the car, I'm only measuring 6v at the connector. I can get a replacement unit cheap enough but it would appear to be working(?)

Do you have corroded contacts causing high resistance in the connector?

No, they look shiny and new.

 

It could be a sign of damaged wire(s) between the tailgate and the main body of the car, I would carefully pull off the rubber boot from the body and check for damage.It could be a sign of damaged wire(s) between the tailgate and the main body of the car, I would carefully pull off the rubber boot from the body and check for damage.

3 hours ago, ChrisTids said:

It could be a sign of damaged wire(s) between the tailgate and the main body of the car, I would carefully pull off the rubber boot from the body and check for damage.It could be a sign of damaged wire(s) between the tailgate and the main body of the car, I would carefully pull off the rubber boot from the body and check for damage.

It was certainly a problem I had on my Roomster.  My local garage patched in a new bit of wire and it was sorted.

Thanks guys. I don't know exactly how broken the wire was but it was certainly properly broken after I had "carefully" removed the rubber boot. New bit of wire soldered in and problem solved.