Starter just clicks...
I had that same problem on my '90 PS190. I replaced the starter, solenoid, battery cables, ignition switch, cleaned every connection possible, etc. One time when it 'did it' on the lake I put a test light right on the starter solenoid where the wire comes from the key (yellow?) switch, turned the key and: intermittent low voltage at the solenoid. As a temporary fix I put a smaller extra solenoid (marine rated) next to the starter that is activated off that wire from the key, that in turn energizes the main starter solenoid. The real fix is to run a new heavier wire from the key switch to the starter solenoid, but my 'temporary' fix is still working fine after about 19 years.
A friend had the same issue, he ran a new wire. Neither of us have had a problem (that one anyway) since.