Aux pump or monovalve? You referred to both, I can't tell which one you mean.

The monovalve doesn't need a fuse, the aux pump should be fused in the hot lead. Disconnect the cable at the pump, turn on the ignition, use a voltmeter or 12 volt test light to find the hot pin of the two in the plug, fuse that wire. Someone on this forum was selling a plug-in kit, search for it if you don't want/can't do the work yourself.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970