if you can get to the back of the switch, you would use a test lamp with the wire connected to a good ground and the pointed end touched to the output of the switch. When the switch is on, touching the output should light up the test lamp. Turning off the switch should turn off the test lamp8/3/24 If the membrane is defective in one or the other pumps, is it repairable? How do I test the switch?
example of tester: https://www.homedepot.com/p/Gardner-Bender-12-Volt-DC-Automotive-Circuit-Tester-GAT-3400/202867876
There are kits for the internal parts of the pump but if your pump is older or in the worst case original, it doesn't pay to try to replace the internal diaphragms and valves. Your model umber is no longer made but there are pretty much exact replacements.