Third brake light, replaced but still broken?

[SamuelL421]

About a week ago, I found that my third brake light (LEDs in the middle) had gone out and that the dashboard "light out" indicator was on. Knowing this to be a common problem, I ordered a new light thinking it would be a simple fix.

After the light arrived earlier today, I removed the old light and attached the new one. Unfortunately it hasn't solved the problem, I still have no third brake light and the dash indicator is still on. So I then tried a multimeter to check the voltage going to the brake light when the pedal is depressed. With the brake pedal pressed down and the other brake lights working, I still get no noticeable voltage to the third brake light (my multimeter is set to 20v DC).

I was thinking that I could possibly test the third brake light outside of the car to see if it is even working correctly. I'm not sure how to go about doing this, does anyone have some advice on the topic? How could I test my third brake light and what sort of power source could I use?

Has anyone else had this or similar problems with the third brake light? Any ideas what to try next?

 

[srhutch]

I tested mine by using a 12v PC router power adapter.

I'm guessing you have a break in a wire somewhere

 

[TheHoff]

The wiring loom along the boot hinge is the likely culprit.

 

[SamuelL421]

Apologies for the extremely delayed response here, but I finally had some downtime to spend with the z4 and a multimeter and I got some odd results... After testing the old 3rd brake light (badly cracked) and the brand new one, both seem to work. I then turned to the wiring itself, with the brake depressed, I had no voltage at the connector. I then moved back along the wire itself and tested again - same result, no voltage. Next I moved back to where the wiring goes through the small rubber boot between the trunk and the body. I pulled back the boot and checked the wires on leading into the body and had the same result again, nothing happening on the multimeter.

Any ideas for what I might try next? I could start replacing fuses, but I feel like something else would be out if a fuse were the issue (everything else on the car works correctly so far as I can tell...)