Very unusual, but it could be the pump is locked up.

It also could be the wire you used as a jumper was too thin or making poor contact in the relay socket. The test you made with the voltmeter is a further indication you may be "barking up the wrong tree." That seems more likely to me, because a direct short or locked-up pump would draw enough current to blow the 25A fuse under the hood.
--
Art Benstein near Baltimore

Wisdom comes with age, but sometimes age comes alone.