[Tommy]

Originally Posted by zzmac

I used the jumper cables and both fans work. When I remove the negative jumper cable the fans don't turn on.
Next step? :-)

That tells me the fan is not properly grounded. It could be at the fan or where it connects to the ground source. This assumes the relay provides +12v and not the ground.

P.S. If you can't find where the ground is bad, you can run a temporary ground wire from the fan(s) to a known good ground to hold you over until it is convenient for a permanent fix.