So here it is guys, I have a Mallory series 50 Magnetic Breakless Igniton now i was on my way back to windsor ramp Sunday morning after the 4th and about 400 ft. or so the boat died, no crank no nothing so i checked my breaker and bingo it was popped, now upon reseting it  the engine would turn but no start so i figured i got no spark now after taking her back to the trailer i verify and sure no spark well the ignition module inside went out so i made the stupid mistake of buying another module on Monday without checking for a  short to ground possibly so i installed, ran a test and start the engine, now the boat starts runs for 10 to 15 second and senario all over again breaker main pops.... I run my module test to see if it was ok only to find out that i f@#$%@&* it up again  I know i have to look for a short somewhere  but my question is, is there a way to protect the module i think  a fuse on the hot going to the module would'nt help since it would still get that spike before it would blow, maybe possibly a zener from the hot going in to the negative going to the engine block or a (MOV)Metal Oxide Varistor in place of the zener has any of you guys had this issue and all im trying to accomplish is protecting that module for me and anyone and save myself those $83 dollars not to mention that it could ruin your weekend since it's not your everyday autozone part.... 

How are the rest of the grounds?  As in block to battery and those connections?   Is the module grounded to the block close to the distributor?  I know you have a magnetic distributor, but I've run a unilite for a long time and every  time I had a module problem it was because the  connections had become corroded, not necessarily the ones for the distributor but the main power and ground, and I use the power filter mentioned above. 

Throw it away & get a junkyard HEI!Rid of the vac advance & add a curve kit & voila!You will never find a hotter sparking,more accurate ignition system,parts are cheap & readily available.Dont waste your money on MSD or mallory hei's.Coils are weak at best & internal bushings & parts are designed to wear out.1 wire on a breaker,your boat wont know how to act,neither will you!theres always crank triggers if ya got a fat wallet. 

Also, just because I read this late and was processing the MOV idea. Varistors I don't beleive are effective at all on DC circuits, unless they have changed since I was in the electronics industry. It would be a good thought, though.

Ray