what is a good way to test for this prob or ? any ideas would help thankyiou james

touch your tongue to the coil wire while holding a 100 watt bulb, have a friend bumb the key...

could any tell me what ign system this mercruiser 7.4 has engine id # is of 773374

Not a good serial number you should have a zero and a letter before the numbers. Probably has Thunderbolt 4 or 5. Weak spark would probably be the coil, the module in the dist will either work or not and the amplifier usually doesn't cause weak spark. Are wires and plugs replaced?

that is on the tag on the motor

Weak spark from coil is most likely a bad coil. Switch it out for $40.

Didn't see the 0F, this engine has the Delco ignition, not Thunderbolt. These coils also go bad and there is a module inside the ignition that goes bad also. This is an automotive ignition and parts are available anywhere.

Merc part # for the coil is #898253T27 and they are $115.20 each and the module which I'm betting is the problem is #811637001 and cost is $133.25 and don't use automotive parts on a boat that's just asking for trouble.

You can easily use an automotive coil as long as you get one for off/road high vibration.