just replaced my ign module in my boat. ran a half a tank of gas thru it and my module went out today? why so soon? it was oem replacement also. 1984 454 330 hp thunderbolt iv

Bad grounding somewhere in the circuit or a bad coil drawing too much current through the module.

+1

and if its mounted to your exhaust manifold riser,,it will over heat it if theirs not enough water going through the riser to keep it cool..manifolds and or risers could be all rusted up inside keeping it from cooling..

the ground wire for the ignition module is on a bolt holding down my alum intake. i just bought brand new msd high vibration coil also

Check the ground between the distributor and the intake also, this can cause issues. Use an ohmmeter between the dist and the block, not the intake manifold.

i will thanks

Good idea Ted but, I would suggest the better way to test the ground is to use a volt meter while the engine is running and check between the distributor and block and the block and ignition module.
Any more than 100 milivolts, under 50 would be preferable and I would be cleaning up grounds. Far more accurate than using an ohm meter.

careful on some coils as they are not compatable with all systems...

Not to go off on a tangent, but if the ECU is currently mounted to the manifold, would it be advisable to move them, say, to the transom with a ground wire?

Pull the cap and make sure its turning. You could of lost the gears (ie. grounded off the gears), in which case whole motor will need to be pulled in order to pull the oil pan and clean out the shavings.