Slide blows fuze

You got it. Since you are sure there is THREE wires going to the motor, then the rocker is responsible for connecting to "in / out function". At the rocker, there will be three wires so you can do your testing as you have done at the motor to check those... to check out your statement about the motor "battery connection" without getting "wet". :-) The only "caveat" is to ensure that your ground test point that you use for your meter is a KNOWN ground. If it isn't, then your results may not prove, "beyond a shadow of doubt", what is happening. :-) Pay attention to any +/- showing on the meter reading.

As you "surmised", if the slide doesn't move during the travel phase but the fuse is blown, the short is likely at the motor (just coming in at the hot), or going from the motor to where ever the fuse is situated / wired.