Brake light problem on passenger side.
 

The right/passenger side brake light did not work and cause the warning "Light Failure". I changed the bulb and still it did not work. I then swap the bulb and the white socket from driver side to passenger side, the passenger side did not work but the driver side worked with bulb and socket of passenger side.

This means the bulb and the white socket is good, but it did not get the power and/or it has bad ground. How do I check and isolate the problem ? I have voltmeter. The wire connector has 5 pins, which pins are for the brake light ?

I'd imagine by testing the working connector on the drivers side you could figure out which pin it is. Have assistant activate brakes while you check each pin, and whichever one turns on and off is the one, then do the check on the same pins on the passenger side.

Have you checked the fuse box on the side of the headlight switch?

Check Fuse Box
 

No, I didn't.

Where is that fuse box located ? On the side panel next to the headlight switch ?

The car is driven by wife, I'll check the fuse tonight.

Thanks

HTN-E430, look in the Index of your Owner's Manual under "Fuses" for the page that shows the locations of 3 separate fuse boxes in your E430. The card in the lid of the main fuse box under the hood, driver's side identifies the circuit protected by a specific fuse. It's likely there are identification cards with the other fuse boxes too.

It works
 

I replaced the 7.5A fuse (fuse #7) on the side of the headlight switch, it did not do anything different. I then swapped the socket with the working bulb from driver side to passenger side, the driver side light up but passenger side did not. I then swapped again and try to seat the socket on the passenger side harder and it works.

The question I have now is how to keep the socket (bulb holder) tightly in contact with the light assembly, if the car hits a bump it may get loose again.