Re: Cooling problem solved now what's wrong with my tach?
My boat came with a blown alternator, and then I blew the diodes on the replacement by turning off at the key before stopping the engine. In both cases, the tachometer would not work. As Faster says, you really need to check that you have a healthy charging voltage - 14V or more.
If not, either the alternator is faulty, or it is not getting the excite voltage via the ignition switch.
Bristol 31.1, San Francisco Bay