See -> overload protection relay also known as OVP - overvoltage protection relay in the link below.

1988 Mercedes-Benz 300SEL Base Sedan - Switches, Motors, Relays, Fuses & Wiring - Page 5

A small door on top flips up providing access to blade fuses inside. There are usually 2 fuses, although earlier versions of this has only 1 fuse.