I'm not absolutely sure, but I believe the OVP only supplies voltage to the systems with sensitive solid state electronics like microprocessors such as the "E" part of the KE Jetronic system, ABS system, and SRS.

As long as any alternator's voltage regulator is functioning properly it should maintain system voltage in the 13.5-14.5 volts range for any load as long as that amp load is less than the alternator's max available at the RPM it is turning.

I don't know what you mean by "upgrade", but your car should have at least one OE auxiliary electric fan in addition to the clutch fan. The clutch fan should be fully tightened at 100C and should be much louder at about 2000 revs when it is engaged. You should test it. The aux. electric fan(s) engage high speed at 105C and shut off at about 100C. If the A/C is engaged a pressure switch will energize the fan(s) at low speed as necessary.

My 190E 2.6 has two aux. electric fans. The W124/M103 models have one of larger diameter due to the taller radiator. I'm not sure if the W126/M103 has one or two.

One of my aux. electric fans failed, and I did a failure analysis... posted the results including photos. Search for threads started by me if you are interested in reviewing.

Duke