I have merc 502's in my boat and the port engine will not turn over as I think the automatic shutoff thinks that the throttle lever is in gear which it isnt.
The cables are a little stiff which I think could be messing with it. but no matter how much I move it around and mess with it when i turn the key it wont even turn over the starter motor and the alarm goes off. Can anyone help me

Does the boat have lanyards on the key switch if it does check those.

Push the neutral detent switch in and try it

Check starter solenoid the one on the top of engine that looks like the ones on trim pump

The Neutral Safety Switch should be part of the shifter assembly. It can easily be bypassed for testing if needed.
What controls do you have?????

It could also be a problem with the kill switch.

to be safe remove the plugs and give it a try,if it still won,t crank you just ruled out the possability of hydro lock.

good idea,many people have replaced a starter motor only to find that it was the slave solenoid.

Start with the basics and make sure your prop spins ( are completely in neutral gear then try to start the engine ) if no go move on to - how about a bad slave soleniod or a bad starter. Can your hand / wrench turn the engine over at the crank ?

I'll throw one out there that messed this boat owner up for a while until I looked at it - a completely 100 % locked up water circ pump and after about 20 or so tries of him trying to spin (start) the engine over - he broke the starter.

Not saying this is your problem but you can never rule anything out when it comes to boats