Early ones had one fuse, later ones had two, interchangeable. Stalling at low idle or fluctuating idle rpms have indicated bad ovps for me on both of my M103 cars. If you can get hold of a known good one to try, it might worth the trouble. Also, and this is beyond my ken, sometimes the circuit on the board inside the relay gets broken and can be resoldered. you might find more information on that by searching the forum.

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1994 E500 199/Gray 82k
84 300D (Salty) Orient Red/Palomino 141k
88 300CE (Ersatzhammer) 904/Java 163k -- Turbo Technics twin turbo kit, AMG Gen I body kit, Sportline steering box and steering wheel, Sportline/Eibach /Bilstein Sport/500E suspension, Quaife LSD in 210 mm diff case, Silver Arrow brakes.
88 300CE Brabus 3.6 199 on Black 44k