The over-voltage protection (OVP) relay in a Mercedes is designed to protect the vehicle's electrical systems, such as the anti-lock braking system, in the event of a voltage surge. This relay is mounted inside a small plastic container situated behind the vehicle's battery. It is easily identifiable by the 10-amp fuse mounted under a clear plastic cover on top of the relay. Replacement OVP relays are available from certified Mercedes-Benz parts resellers.
Drive the car onto a flat surface and shift the transmission into park. Turn off the engine and depress the parking brake pedal. Pop open the bonnet.
Locate the OVP relay box. It is made from black plastic and is located directly behind the vehicle's battery.
Remove the cover from the OVP relay box and pop open the clear plastic cover holding the 10-amp fuse to the relay. Remove the fuse from the relay. Remove the relay from the relay box.