How do you test an OVP Relay?
 

I'm hopping my hard start and rough idle are symptoms of a faulty OVP Relay. Looking at the prices online for one I'd rather test this one to make 100% sure that that is what needs to be replaced.

If you can tell me what to do and what to look for I would appreciate it. Thanks!

With ageing the solder joints will go bad in the OVP as well as the Fuel Pump relay,they can be re soldered and all is operating again.
To test the OVP start a cold engine, remove the OVP ,the RPM's will drop down ,insert back RMPs back to normal as well as the ABS light going out.
mak
300se

I would not recommend removing the OVP with the car running!!!!

86 300E, when the OVP relay in my parents' 1995 E320 went bad it made a buzzing sound and the engine idled poorly. Fortunately I have a 1995 E320 and swapped my OVP relay to confirm the problem.

On a 1995 E320 the OVP relay is behind the battery. Not sure if it's the same location on your car.