This week we had a Mercedes-Benz R-Class which had a problem with one of the low beams not working.

The owner installed a new light bulb but that didn't fix the problem.

Mercedes new light bulb not working

Upon further diagnostics we found that the headlight fuse kept blowing when you either turn on the ignition or when you turn on the headlight.

Since most Mercedes vehicles have auto lights the fuse will blow as the lights turn on automatically.


The problem can be the wires inside the headlight assembley. The wires may overheat. Eventually the insulation cranks and comes off.

The problem is because these wires get too hot which is part of the reason why the insulation gets damaged.

damaged dry roten wires headlight

Once the wires are exposed they short which causes the headlight fuse to keep blowing.

A temporary solution is to insulate the wires. While this may work, it is not the ideal solution.

repair mercedes low beam not working

Ideally you want to replace the wire harness which requires the removal of the headlight unit and may even require removing the lens from the headlight.

If your are having problems with your Mercedes-Benz headlight not working after replacing the bulb check the connector to the headlight assembley.

If the connector is not damaged or corroded and you know the bulb is new other possible issues may be:

  • damaged wire harness
  • defective headlight switch
  • faulty SAM module