sl55er

Hello all I have a weird problem on my 2004 sl500. when I apply my brakes the upper brake lights are not coming on but the 3rd brake light is still working fine. I checked the bulb sockets with my volt meter only getting about 1.8 volts. also checked the fuse for brake (f24) and i have 14 volts there . both left and right are reading 1.8. Anybody have any ideas?

alk247

Are you getting a fault message regarding these bulbs?

sl55er

Yes messages telling me bulbs are out.

alk247

So they are burned. Replace them, and voltage would go back to normal. There are control circuits that remove power from burned bulbs. This is why it is impossible just to replace bulbs with LEDs in our cars.

sl55er

They are not burned out that is the problem..... I swapped bulbs from my other sl500 no change. And bench tested them all, very bright

alk247

Then it is likely there is no contact in the sockets. Try to put resistor across wires upstream of the bulb and see if it changes anything. Correct resistor value is approximatelyy 150/Bulb rated power.

Rudeney

First of all, the upper bulbs should not illuminate unless the lower LED bars are not working. The halogen bulbs in the upper corner of the tail lights are only used as rear fog lights (driver's side only) and as an alternate brake light if the LEDs fail. All exterior lighting is electronically controlled by the SAMs so there are no fuses. The SAM monitors current draw on each bulb circuit and if it detects a problem (gih with a short or low with a bad bulb) it will shut it down. This is why you can't check voltage with a meter. My advice is to check the wiring to the tail light assembly to find out why the LEDs are not working.