OVP is OverVoltage Protection. It's a relay with a fuse on top of the can. It is designed to protect the electronic gizmos such as the ABS computer and the engine management computer(s) if the alternator runs away and produces too high of voltage, or voltage spikes from jump starting.

The OVP relay has a bad habit of going bad in random and intermittent ways. When troubleshooting anything that seems flaky or intermittent, the OVP is something that should be replaced. In a Gen II W126, a clue your OVP relay is inoperative is an ABS light that won't clear or flicks on and off as you drive.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]