Last week, my 88 300E's OVP failed after a little over 3 years of service. It was KAE brand. Post mortem disassembly revealed bad corrosion in the lower part of the relay & a couple of failed solder joints. I recall driving down some semi-flooded streets during the stormy winter of 2004-05, after which the car stalled a few times. Perhaps that's when moisture got inside & started the corrosion.

One sign that the relay was going bad: the "check engine" light would sometimes glow with the ignition shut off. Finally, one morning, the ABS light came on, the check engine light stopped working, and the car was hard to start when cold, but easy to start once warmed up. I checked both blade fuses, & neither was blown.

I wish that the OVP relays were engineered & built better. They can cause a variety of nasty, hard to diagnose problems.