[mitiempo]

Buy a better switch. The Whale or the Waterwitch switches are reliable and have no moving parts.

Whale: Whale Marine - Products

Waterwitch: https://www.waterwitchinc.com/new/SiteElements/Pages/SecondaryPages/Products/BilgeSwitches.html

I prefer the Whale as it is smaller.

Having said that your problem may be a bad connection. Switches in my experience either work or they don't. It's possible that you have a connection that is either corroded or bad. If only a strand or 2 are making a connection the pump will probably turn slowly but not enough current can pass to run it properly. I would check or renew all connections in the float switch side.

 

[mitiempo]

Which size pump do you have? 9 amps is the recommended fuse for a Rule 1500, any pump smaller needs a smaller fuse:

1100 - 6 amps
1000 - 5 amps
800 - 5 amps
500 - 2.5 amps
360 - 2.5 amps

The larger pumps need larger fuses starting with the Rule 2000 at 15 amps and then going to 25 amps for the 3700 and 3800.


I also think it is a connection problem.