I haven't found any easy test with a multimeter. However in my case, the test was simpler. With the problem present (low idle, dead tach)... tap the OVP relay with a screwdriver lightly. If the symptoms suddenly disappear, the OVP is bad.

The discolored pins really don't mean much unless they're really corroded, or have green crud on them. For your VOM, measure the battery voltage, select a range that allows easy reading of 12V from the battery.