In the pic as I will give you heads up the black lead with the big eyelet on it needs a good clean ground connection, no corrosion or painted surface to attach to. If you do not have a good ground connection with the new module - you still will have no spark.

Also Merc had 2 or 3 service bulletins back in the 90's about the upgraded version of the module and it was wise to change them out. Also might want to get another rotor just in case you break it pulling off to replace the module. You do not have to pull the distributor to change the module. It is a very simple R & R and hopefully your fix. Again the way to screw it up is not to have a good ground connection.

It was the module.

What would cause the module to go out? I think it just did it again.

Post your serial # for the engine as this will provide the exact ignition set up you have from mercruiser thru out their serial # breaks. if I recall the later years 502's did not use the ignition sensor like shown in post 9 as I forgot beforehand. The next important question is your engine and ignition set up totally OEM Mercruiser stock ?

They did have the module under the distributor cap along with a pick up coil. You might have a BAD PICK UP COIL.

Also heat, high electrical resistance can cause failure to ignition parts. Also weak batteries, poor connections, loose connections especially battery connections, corrosion, bad grounds, undersize wiring and undersize battery cables. Also an over charging battery can hurt ignition components. Improper testing for spark on ignition components can hurt them as well.

Make sure your cap and rotor are in really shape as well.

What red wire did you check for power at? Ignition power in a merc harness is purple.