Disconnect the cables from the engine. Does the wheel now turn freely or still stiff?
As said above, does the engine move freely with them disconnected?
I'm assuming that the engine ends of the cables run through tubes in the engine mounting? Likelihood is that old grease & crap has built up & they're seized or partially seized. They need cleaning out on a regular basis.
If that's the case you may need to knock them out. Use plenty of penetrating fluid (not WD40, Duck Oil or PlusGas are much better) a block of wood to protect the ends & don't go mad.
You might find that one of the tubes has been damaged & is now too tight. In that case - and it will also help if the crud is solid - an expanding reamer will be the answer.
(Mine is a 135hp Mercury with twin steering cables. Guess how I learnt the above?)
BTW DO NOT
try & get things moving by forcing the steering wheel as you are very likely to break the helm & will have to buy a new one.
This might be worth a read: Siezed steering