1987 Evinrude 90 hp overheat horn

[Champion88]

I have a friend that has a 1987 Evinrude 90 hp E90TLCUR. He had a problem with it overheating so we replaced the water pump, thermostats and the relief valves. It now seems to cool, but every once in a while his overheat alarm will go off (constant alarm, not intermittent), and it not consistant, it happens sometimes at full throttle, and sometimes at idle.
The water pump was complete when we replaced it, it hadn't come apart and plugged up the water passages.
Could this be caused by the temperature switch? or what else?

[j archer]

I have that issue the first couple runs of the year and then does not do it for the rest of the fishing season. I was running mine in the drive yesterday and the buzzer went off I shut it off let it cool restarted let it run and did not go back off, any ideas on that?