Fans can draw quite a bit of current, but I guess the Otter switch is appropriately sized to operate well enough, however if it fails as they sometimes do, it can be handy to wire in a manual override switch...
The idea of the switch is that if the Otter switch fails at some inconvenient moment and the engine begins to overheat, you can flick the switch and cool things down a tad.
Pretty sure that instructions/diagram may be found on GoMoG in the workshop manual should you be interested in fitting an override switch..?
My mid 80`s +8 Otter switch maintains the water temp at circa 90deg C, though perhaps in general lean burn technology may have been introduced around the mid 80`s which required engines to run hotter to clean up on their emissions thus 120 deg may be entirely normal for your engine..?
