Newbie questions, 1st spa, OK. Two magnetek 3hp pumps one is working fine, the other I hear trying to click on but won't start. I tried sticking my fingers in impeller(power off) to see if stuck, I can't tell.How to tell the diff between bad pump or motor, should I replace as unit? Thnaks

I would start by removing the motor from the spa, and bench testing the unit. See if it will run with no load on it. Also with the pump removed, you will have EZ access to the impeller to see if it turns by hand. If it moves freely by hand, but it just jumps a little with each click and hums, then you may have a bad bearing. If it doesn't turn at all by hand, you can try to have it rebuilt, but most often they seize from rust and you will end up having to replace the whole unit anyway.