HELP Older 65hp red stripe electrical problem

"On my last outing my son reve

"On my last outing my son reversed polarity on my battery and tried to start the motor.(as a result of this i found there was no spark. After i checked it out i replaced the rectifier and now have spark and the engine only fires and runs while the key is held in the cranking position all the while the starter is engaged, when it falls back to the run position it kills the motor.I have tried removing the positive starter wire while it is running with the same result ( this also kills the motor. (Why do i only have spark when the starter is engaged.)Any help would be appreciated.
thanks (Ken)"

Sounds like you now have a bad

Sounds like you now have a bad ignition switch.

"Ken, Does that motor have a d

"Ken, Does that motor have a distributor? Sometimes on the Dissy models, when the trigger is bad it will do that. Since triggers are expensive, you need to thoroughly check out the otehr ignition components and wiring."

"Chris, a red stripe 65hp is l

"Chris, a red stripe 65hp is likely around a 67-71 model and distributerless MERCURY motors did not come out untill the mid / late 80's."