Took a look at the wire diagram and the brake light switch goes to the light switch/fuse panel, and the wired from the brake lights go to the light switch/fuse panel as well. I have looked at the fuse and its good but the voltage is non existent when I hit the brake pedal so it has to be another bad switch, I've gone through 2, one was a cheapo knock off, and the other was MB switch from the dealer. Next ill try to reset the connectors to the electronic brake controller. Ill also check the brake booster switch ( a TSB said if the O-ring is not present to replace the Brake Booster....

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1999 E300D OM606, 278,000 km (Daily)
1984 Camry Turbo-D, 319,000 mi (Sold)
1992 300D OM602, ~450,000 mi (Sold, Blown Head)
1999 F250 7.3 Powerstroke, 243,000 mi (Sold)
1996 VW Passat TDI 110,000 mi (Sold) "The first Diesel"

Hang a incandescent test light ( or vehicle marker light ) on both sides of the brake light switch. One should be on while the car is running and the other when brake is pressed.

Drive around to test.

Is the switch properly adjusted? If the plunger does not extend enough you won't have brake lights. Just be be sure, is this a switch that mounts to the brake peddle or a brake booster mounted switch under the hood?

I know that BAS Brake Assist has a booster mounted switch but i have not researched this system.