If the OVP relay is bad then the ABS light will come on. Not sure if ABS is fitted on your model though and other things could be the cause. Does removing the fuse when the engine is running cause any change? If not the relay is suspect. If you do get some kind of change then you can assume it is working at least some of the time.
I successfully opened up the relay and ran a hot soldering iron over each of the joints on the pcb inside. That fixed the problem.
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)