With no information, making a few educated guesses.
The wire to the choke solenoid is connected a small terminal strip, could be a white wire. Connect a meter to the terminal strip and see if 12 volts is present with key on and choke switch pressed. If you see 12 volts, the choke solenoid is bad or the solenoid slug with the small cable to the choke plate is missing or hanging free of the solenoid. Need a motor serial number to ID the parts.
If no 12 volts, start backing up to the choke switch after checking the the switch for voltage on both sides. Wiring on these old Mercs can fall apart.
All the above is without know what motor you have.
Rubber cover is part number 30027
Choke switch is P/N 29567