Check the ground. Run a jumper wire from the ground side of the pump (typically Brown)to a good ground or the negative post of the battery to see if the pump operates. I had the same problem an at first couldn't get it to work by jumping it. But it did after I replaced the relay. The ground was bad and the high resistance might have contributed to the demise of the relay.

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1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T