Ignition blowing fuse at 3500 rpm

Not sure what's up, but my Vector an issue blowing the main fuse on the hot feed to the ignition switch when I reach 3500-4000 rpm. I haven't delved too deeply into it, other than examining wiring diagrams. It is a carbureted 502 with the blue MSD marine 6m-2L multi-fire ignition. I'm thinking it could be a choke wire issue, or possibly the MSD controller. It was running fine one trip, then the next it started blowing the fuse. Seems to run fine at 3000 and below. Anyone have any ideas? Thanks in advance for your help and smartassed comments. ..... Dale

What's the volt meter say? Maybe when the alternator is spinning that fast it's pumping out to many volts? Just a thought.

Is something moving when the gets to that rpm and shorts out the 12v