You have a short somewhere. Quite possibly in the feed to the control. In trying to find a short, you have to look at and follow the wiring harnesses and look for obvious damage to the harness. Sometimes simply moving a harness around will fix the problem. I would suggest you substitute a 5A automotive circuit breaker in place of the fuse. It will be clicking on and off but it will allow you to do some troubleshooting with the circuit basically powered up.
Sometimes you can take a magnetic compass and use it as a short finder. Simply follow the wiring with it with the circuit powered up. The needle will point towards the location of the short. So, if you put the compass on the harness at the switch unit it will likely point away from the switch. If you go to the main pump/controller unit and place the compass on the harness there, you will probably find the needle pointing back at the switch. So you know the short is between those two points. Then you can start working your way one way or the other. Once the compass changes direction and starts pointing back the other way, you know you have passed the short.
2005 Newmar Kountry Star Gas 3742
Workhorse W24, 8.1L/Allison 5-spd
JT, Em & the boys, Kong and George (rescued grey tabbies)