Frustrated

Hello friends: I desperately need your advice. I have a1990 15hp Johnson outboard. My shade tree mechanic has replaced all the vital parts in an effort to fix it and we have come to a complete wall! Carburetor replaced, coil, wiring, plugs, water pump, kill switch. There is good compression, good fire, fuel lines all replaced. But still no internal combustion. I read somewhere there is a neutral switch. If it's bad, no way it will start. Does anyone have any suggestions for my mechanic?
Here is what my mechanic said:
"1/2) Terry I'm stumped I have thrown the book at it and we still can't make it run now we have it all compression fuel and fire and still no internal combustion(2/2) n. It won't start no matter what I do it may need points but they looked great and I don't know.......... it's the damnedest thing
Terry I have been over it 10 times I'm at a wall bud everything is good from what I see and I can't get anywhere with this thing"

So what is your motor doing / not doing ??

Need a model #. Electric Neutral safety switch on that motor ONLY stops the Electric starter motor from turning with the motor in gear. There is a mechanical neutral safety switch, but that only locks the recoil starter when the throttle is advanced to far in gear. The tether switch should not be the problem because you have spark. Have you checked the flywheel key. 1990 model 15 hp motors do not have points.

Thanks for your reply. I have forwarded your info to my mechanic. When he responds I will forward his words to you. Thanks again!