I have a 1987 420SEL with cold start problem. I wanted to know where exactly is the OVP relay located ? Other question, my cruise control is malfunctioning and I'm suspecting it's the electronic amp that's mounted under the dash on driver's side. There's more than one box under my dash and I'm not sure which one it is or how to identify it. THANKS !

I don't know if yours is in the same spot, but on my 88 300SE: Open the hood and stand alongside the driver's fender back toward the windshield. For lack of a better description, the engine area is separated from the windshield area by a verical metal "wall". In the area between the windshield and the "wall" you'll see all manner of relays. The OVP is the one with a clear plastic top that easily flips up. You'll see a single 10amp fuse. That's the OVP. On mine if you're on the driver's side it's the relay next closest to you from the infamous one stamped "KLIMA".

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Thanks,
Ron Brooks