Brake Light Switch Failure: Causes and Fixes

Hello fellow DIY enthusiasts!

I would like to share a brief report about a defect in the brake light switch in a Golf 4 TDI manufactured in October 1998.

The friendly person said they would break down frequently, but that it happened again within 2 months, which made me suspicious.
Okay, first, I disconnected the wiring for the aftermarket trailer hitch and pulled the connectors from the taillights. I measured for a short circuit at the brake light switch connector. After connecting the trailer hitch wiring and plugging the connectors back into the taillights, I measured a current draw of 3.7A, which seems okay. Now I've discovered that the third brake light (the LED bar) isn't working. I opened the tailgate, and the fuse for the brake light circuit blew (the brake light switch connector had been temporarily bridged for testing).
Now, I can highly recommend that everyone, in the event of a defect in the brake light circuit, checks the left cable conduit from the interior to the tailgate, specifically the rubber grommet. In my Golf 4, which was only 6 years old, almost all the insulation at the bend was broken!
The wiring to the LEDs was completely broken, and I don't want to know what could have happened through those exposed wires!

The wires were first re-soldered, then insulated with heat-shrink tubing and additionally wrapped with electrical tape. If it breaks again at the solder joint, a new wiring harness will be installed for 65 euros!

Best regards, Ferdi.

"I'm familiar with that too; those are the areas with inherent weaknesses. I usually use LAPP cables there. I have some leftover pieces from a previous project. They're super flexible and have fine strands. However, even they have their limits at sub-zero temperatures. There are no affordable cables that are approved for moving applications and temperatures below minus 5°C."
I would strongly advise against working on the wiring harness when the ambient temperature is below plus 5°C. The insulation can become brittle, and that's when corrosion (green deposits) can start to form.

Best regards, Robert.