Brake light dead

[SirHiss]

I've got a weird problem with my left brake light dying.

I was having issues with it a while back so I installed the Mercedes looms as explained here: https://xoutpost.com/bmw-sav-forums/...light-fix.html

They were working fine for a while but then the left bulb died and I cannot figure out why!

I have tested all connections for continuity. All looks good. I have tested the voltage across the bulb holder itself with a foot on the brake and here's the weird thing... With no bulb in it, it's getting voltage. But when I put the bulb in, it gets no voltage.

I am so confused and defeated.