Engine will not shut down

Hi Guys , got a good one this time. Most people have problems starting a engine mine will not shut down.
I have twin 2004 Yamaha 150 HPDI . When I turn the key off the engine will continue to runs and idles OK for about 15 sec. to 30 sec.
than shuts down with the key in the off position. The switch control panel was changed with no help. Any ideas ????

Loose ground somewhere.

Does the kill switch cord do the same?

I had two problems and both was fixed. I been also having problems with #2 engine not staring about every 3rd trip out. After working the throttle and switch a number of times it would start. Also been having the Engine #1 not shutting down. Time to call my mechanic with his computer. The engines checked good and he said it the switch assy. The switch ?. how could that me . It's just a on off switch like a car , right ?. Not in this world today. There is a sealed circuit board behind the switch ,with the horn and a bunch of who knows what. Anyway $300 later and both problems are fixed. Hope you guys don't run into this .