I don't think your OVP relay is the problem. It would cause intermittant not regular ABS light malfuction. At the speed you are getting the light the system does a self test on the wheel sensors. You undoubtably have a wheel speed sensor problem.

I'm guessing that you have a spark plug resistor problem for your running problem. They result in intermittant single cylinder misfires. They are easily identified with an ignition scope.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician