I've been thinking about the voltage idea a bit more and I think there might be something going on.

When I turn on my headlights the check engine light comes on, occasionally the rear defroster light will blink when turned on, and driving home tonight I had a hard time seeing the road, the headlights seemed a bit more dim than usual.

Since I've replaced the OVP, where do I go from here to determine if it is a voltage issue?