2 small bulbs in rear tailight assembly

[rmmchl]

one of the small bulbs in the rear light assembly  is the tail light. Does anyone know what the other small bulb is for. The 3 large bulbs seem to be for the turn signal, brake light, and maybe reverse light??  does anyone know the Mercedes part number for the small bulbs. I bought mine from auto parts store, , but they can come loose real easy. Just wondering if Mercedes made a special one, that fit tighter

[JamesL]

https://www.sl113.org/wiki/Electrical/TailLights

Outmost is the turn signal
Innermost is Brakes
Middle upper is rear/tail light
Middle lower is reversing

Fog light?
You don't need a MB part number as they are a standard fitment from any parts store
https://www.sl113.org/wiki/Electrical/TailLights

You can buy LED replacements that are brighter - but turn signals require extra wiring/relay work.
https://www.sl113.org/forums/index.php?topic=22863.0
https://www.sl113.org/forums/index.php?topic=26748.msg191385#msg191385

[Pawel66]

They may come lose perhaps because they are 50 years old. Try to squeeze the base a bit here or there or better bend the spring base more up than it is now (do not remember if there is that spring there - I think there is, it is where the bulb gets the + at the bottom. It presses up so that the two "nipples" on the bulb engage in the slots of the base after you turn the bulb. After 50 years of being pressed these springs lose their "umpf" a bit, you need to bend them back up to have more tension. Just be gentle not to break them off.

[ejboyd5]

Without a picture it is impossible to be 100% accurate, but you are probably referring to the 5W lamps intended to illuminate the one side of a car closest to a traffic lane when parked on a dark roadside. Activated through the headlight switch, these lamps are such a small consumer that they can be safely left illuminated all night without fear of draining the battery.