The OVP relay plays no part in the starter operation. If the motor cranks but won't fire then the OVP relay is a possibility.
BTW David, the 52 45 and 67 45 OVP relays are for 93 on HFM-SFI systems. There are two more relays for the earlier cars and they all cause problems.
Also, viewing ones head lights is not a great way to tell about battery condition. If you view them while cranking they can tell a lot. If they go out while cranking the battery is not sufficient (or the circuit too poor). If they stay the same while trying to crank the starter is not being engaged. The headlights take about 8amps the starter about 150-250 (depending on gas or diesel 4cyl or V8 etc).
Bosch Master, ASE Master, L1
33 years MB technician