I had to look at your profile to see what car you have. On your 190, it's near the battery. You will see 2 black relays, both about the size of a pack of smokes (not half that size as previously posted). One will say "KLIMA" on top, it's NOT that one, it's the other one. KLIMA is for the AC compressor clutch, the other one is the fuel pump relay.

Gilly