No need for a larger alternator. I ran electric fan only on my '73 220D for over six years, on on my '71 250C (with transplanted M115) since '06, a '73 280 and on my '74 280C here in the desert Southwest and used the stock 35 amp alternator and battery on all of them.

Use a thermostatically controlled relay.

The 16" fans only pull about 11 amps at initial start-up and drop to about 6 amps during run mode. They CAN be run using 16 ga. wire but I prefer using 12 ga. for peace of mind.

Haven't tried all electric on my M117 and probably won't because that alloy engine gets hot FAST!

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now