Re: johnson 135 temp
On the 135hp model, if the engine starts to overheat, but before it gets too hot to do any damage, that sensor will ground out and cause a overheat warning horn within the control box to sound which warns you to shut the engine down.
To test the horn, engine not running but with the key in the ON position, ground out that wire at the cylinder head. The horn should sound. If it soes not, find out why as that's the only warning you'll get if the engine starts to overheat.
