Are you using glass replacement fuses or the original type with the wire wrapped around a ceramic insert? The glass fuses sound like a good idea, but can cause all kinds of problems, so stick with the original type.

The two pervious posts had good ideas on troubleshooting - clean the contacts good with a wire brush. I would also take the fuse box out and clean all wire connections on the back.

Dirty fuse contacts can cause this problem as well.

I suggest you disconnect the battery, and then clean the fuse contacts with a wire brush.

Good luck!
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If you listen to the radio in Portland, OR, you may know me as "Portland's Favorite Soul Brother!"

First I would measure the voltage output of the alternator. It hasn't happened to me on a Volvo, but I did have a bad voltage regulator once which put out a high voltage and caused overloads throughout the electrical system. Burned out the headlights too. If the voltage was too high, the pump would draw too much current.

A more likely problem is the pump going bad and drawing too much current. Place an ammeter in series with the main pump power wire and run the car. The pump should draw a maximum of 6.5 amps. If more, the pump is going out.

The last possibility that I can think of is a short in the wiring to the pump.