Low Wire Voltage

mehranalmasi

Hi,
I am upgrading a swimming pool and have noticed a problem with current to one of the pumps.
Basically there are two pumps for the pool. One for filtering and one for the sweeper. The pump connected to the filtering wiring does not run but if I connect the same pump to the sweeper wiring, it works. I could see that both wires going to the filtering pump have power but when I looked closer and compared to the reading on the sweeper wiring, the filtering lines register a bit less current.

They both used to work. So the question is: could a slightly less reading on the voltmeter be the cause? if so how can I find the source of this problem? I have used a sand paper to clean all the contacts between the pump and the switch.

thanks.
Mehran