If the engine runs fine w/o the kill switch but lousy with it installed.... I'd a$$ume that either the new switch is faulty... OR... you have something wired improperly.

Ok boats in the water and running great I changed the switch again to a new one and it works fine however now when I take the boat out of forward to the neutral position the motor stalls ??

From what you've had to say, I a$$ume that you have two (2) new shift interrupt switches on hand and both are acting up? If so.............

With the engine NOT running, have yourself in a position whereas you can easily spin the propeller so as to have the engine shift properly (align the shifter lobes).

Have someone slowly shift the engine into and out of gear while you observe the shift switch function. It sounds like the shift switch is being jammed in the contact position (button pressed down).

This is usually caused by:

1 - Improperly adjusted shift cable. (Easily tested simply by disconnecting the shift cable and shifting the actual engine's shift linkage by hand.)

2 - Salt corrosion build up at the nylon bushings of the engine's shift linkages. (This is what I have found to be a never ending problem unless greased properly with anti-corrosive grease.)

3 - Lower unit problems... shift rod jamming. (Lets hope not)