Ok, seems to be my month of working on the 1997's W210 that I own.

Question...1997 W210 Sport....right headlight went dead and I have replaced the bulb but still no light....could it be the ballast and if so, is there a way to test to see if the ballast is working or not? Again, have already replaced the light bulb. Fuse is/was good. I replaced the fuse just for sh#^ and giggles.
Thanks to all....

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Norm K.
'97 E420 Sport
'06 E350 Sedan
'67 Mustang Coupe
'70 F-250
'15 VW Jetta

You would need a wiring diagram to make sure there is power and ground at the ballast.

Swapping left to right would be a good ballast test.

I think you can read codes through a scan tool. My 97 SL320 has xenon lamps with beam leveling.

I have some xenon parts headlights from a E420, I'll have a look when I get a chance to see what they look like.

Swapping left to right or vice versa is always my go to test when there is a part malfunctioning that is easy to change out, like a light. First test the old bulb in left head light to see if its actually out. If it doesn't turn on, put the new bulb in the left head light. Then confirm that its the actual ballast by disconnecting the ballast and swap left and right.

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1990 190E 3.0L

Ditto....

I just looked at the parts headlights I have. The ballast has 2 cables. One goes to the headlight bulb and the other has 2 wires ( power and ground ) There is an auto leveling motor but that is in its own cable.

When testing for incoming power and ground, be sure to use a incandescent test light that applies a load. A LED test light / digital meter do not apply much of a load and a marginal circuit will test good.