The OVP or Over Voltage Protection relay prevents sensitive and expensive components from getting fried due to a current surge or something of that sort.

The earlier "defective" units had loose solder joints that would cause hot start issues, rough idles, and such, but you can pull the whole unit off and it won't prevent your vehicle from operating. These units have a fuse on the top, and a blown one would be the culprit to a rough idle issue.

Anyway, I would look elsewhere for the problem...it ain't the OVP.

Also I don't understand "rear brake pad light"? The sensors are generally attached to the fronts only, and don't indicate which pads are in need of replacement.

Speedo gone out? Is yours an electronic unit? Didn't think they were until later (my 93 is mechanical).

I believe the pad light and the speedo are isolated issues. I would start by checking fuses first...it's the easiest (and cheapest) place to start...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car