What part am I missing on the taillight?
 

On the taillight assembly, you put the bulbs in and there's a shiny silver metal springy tab that the bottom of the bulb hits to keep it secure, shown at #1 on the photo. For another bulb area shown at #2, that shiny silver tab is missing.

What would the name of that piece be and where could I get one? Without it, the bulb is really loose and wobbly.

Thanks,

1991 300d 220k

That cavity is for the rear foglight.
Depending on the year, you may have one in the left side but there is not one in the right side.
If you wanted to add rear foglights on that side you would probably have to get a scrap assembly to get the contact as they are probably not available separately.

So there's not supposed to be a tab on that one?
 

So you're saying that side (it's the passenger side of the car) never had a silver tab in that spot to begin with? If so that would be good because then it's one less thing I have to do!

Thanks.

The bottom tab is the +12V contact. It’s not there to support the bulb. The silver plate provides the ground.

If/when you get illumination system warnings but the bulbs all light, check that the plastic tabs on the tail light holder grip the silver strip tightly. As the plastic tabs deform, the silver tab lifts the bulbs away from good contact with the tab.

Sixto
98 E320s sedan and wagon
02 C320 wagon

So in that case....
 

If that's the case, then does that bulb holder for that position need a metal tab like the others? The other guy was alluding to that particular slot doesn't need one, but the bulb is too loose for its own good in there. I'll have to double check but I think it currently lights up without that metal tab being there.

Yes, on the 124 no bulb is meant to be in that position.

It's not possible for the bulb to illuminate with no 12V+ contact. The tab/contact also functions as a spring to hold it in place, that's why it's loose.

I keep spare bulbs in the empty socket.