If you need to swap out incandescent to LED, you're leaving an issue that you should probably resolve.

That's very odd that the beacon detachment allows MB to function - cause doesn't the beacon activate as soon as you lock ball three? Beacons would already be on before that solenoid kick.

My next guess would be to try starting a game with the glass off and dropping a ball directly into the three kickers - see if any of those trip your fuse on their own outside of multi ball - that might get you a solenoid/wire to look into.

Alternatively - get the beacons lit and try other controlled/switches solenoids to see if it's an issue there (like light them and try the kickback or Jagov)...