[dpvu]

The only fuse (if any) will be outside your gearbox. It will be on the wire between the battery and gearbox and is usually on the red wire. It may be in a small case and is a small glass tube. If you have one, check that the wire inside is still in tact. You have a connection with the black wire which is good. The red wire should be connected when you pull the trigger. The selector switch is not the issue as that doesn't actually have anything to do with your wiring.

If it's not a fuse problem, I suspect your switch assembly has become worn and this will require you to open the gearbox. When you open it you will see a small box the red wires are soldered to. This is the switch assembly. There are 2 metal contacts at the top and when you pull the trigger, it should move a small piece between those 2 contacts to complete the circuit. In your case, the contacts may have been bent or have worn out. Worse case scenario is you need a new switch assembly, which is an easy fix and is only about $30.