You need to search the database.
You'll find a massive amount of information regarding the OVP.
Simply put, the best way to test the OVP bearing in mind it's relatively low price, is to change it. The early ones are exhibiting faults now anyway.
If you have only 1 fuse on top of the OVP it's an old one, newer ones have two fuses.
If the fuse has blown, you will have other warning lights on the dash anyway. Do you have the SRS or ABS light on?
But the OVP also influences engine starting under certain conditions too.
1. Search the database here.
2. Check to see if yoour OVP has 1 or two fuses.
3 If it has only 1, buy a new one.
Your car may thank you for it.
1994 E200 Wagon 111,000 miles