" seacraft,
I know nothing
" seacraft,
I know nothing about the engine you are talking about, but I have a few ideas:
The key to this, I think, is to figure out what your speedometer and tach have in common, determine where the signal comes from:
If they bothe are getting a signal from the engine, then start by making sure that if they get power/ground from somewhere other than the wiring harness that the power/ground is there; check all connections from the speed/tach back to the engine and troubleshoot there etc.. etc.. this will probably require a service manual on the engine.
If the "sending unit" for the speedometer is located on the transom of the boat; there will be a tube running up to the speedometer. In this case I think the only thing that your tach and speedometer should have in common is a power supply. Figure out where the power supply (and/or ground) is coming from and you should find a bad connection there.
Jon "