It could be the OVP relay or the voltage regulator. If you lose the OVP relay completely, you'll have poor idle and no AC until you fit a new one. Basically what you're experiencing intermittently now. If you lose the voltage regulator completely you'll run down your battery pretty quickly. If things like AC blower and headlights aren't phased when the ABS light comes on then your diagnosis of OVP relay is probably accurate.

The innards of the OVP relay can be resoldered. I'd try that given the intermittent nature of the problem.

Sixto
... stay tuned