Ducati Voltage Regulator fuse

The wiring AFTER the regulator is part of the Airframe and NOT the Engine.
This info would be covered in the Aircraft Manual.  What Aircraft ???

What do you mean by " Won't Start" ???
It cranks forever and never Starts???
It doesn't Crank at all ???

Be more specific. Details!!!

What Bill said:  Need more details!  

The following video may help:  https://www.rotax-owner.com/en/videos-topmenu/rotax-minute/404-charging

Blowing the 30 amp fuse means you have an overload (Short???) in the house(Airframe) wiring.
It has little to nothing to do with the Regulator.
The regulator's main purpose is to re-charge the Battery AFTER Starting.
The regulator has nothing to do with Starting the engine.
You could completely remove the Regulator and still start and run the engine.

Blowing a Fuse is One Problem.
The Engine not starting is a different problem.
The problem in the Aircraft Wiring is the common element in both problems.

What was the last thing you did before the problem started???

I discovered that the capacitor that protects the VR was miss-wired with a reverse polarity.  I have ordered a new one.

The engine cranks over nicely but will not fire.  It started fine the day before the capacitor shorted out but now won't fire.  It makes sense that the two issues (capacitor & starting) are not related but just coincidence.  What should I check for the starting issue?  

Starting (and Running) need Air, Fuel, Squeeze, and Spark.
Air and Squeeze are probably fine so I would look at Fuel and Spark first.

Try some starting fluid. (Both Carbs!)
If it fires momentarily you have a fuel issue.
If it doesn't make noise, You have a spark problem.