posted 06-05-2007 07:18 PM ET (US)
You can get a tachometer for a used 2001 Yamaha 90-HP outboard motor from just about any seller of marine instruments. However, if you want an OEM gauge that will come with the correct harness and connectors, you probably should look for a vendor who sells OEM Yamaha parts and accessories.Most of the time on a motor of 90-HP the manufacturer has made provisions for including a tachometer in the rigging of the motor, and there will be a wire and connector in the standard wiring harness that is ready to accept connection of a tachometer.
If you don't want to use an OEM tachometer, just get an aftermarket tachometer. They come with instructions on how to install them.
Most of the information in this discussion area is about the electrical configuration of vessel systems, and we don't really concentrate on trying to compile lists of where to buy things like tachometers.
I am not sure of what your definition of "install straight to the motor" is, exactly, but I can tell you that the tachometer connects to the motor. Whether or not the wiring is pre-existing in the harness you already have, I cannot tell you. But if the wiring is not already installed, it is not hard to run a wire from the tachometer to the motor.
I think it is better to get a tachometer with all the proper connectors for installation, or, at the least, if it is available, to buy the proper connectors and rig them to your own tachometer. My feeling is the less haywire in a boat, the better.
Yamaha makes a nice multi-function gauge set which includes a tachometer, a trim gauge, and some oil level warning anunciators. This is an expensive gauge, but it is a nice addition to the rigging. Or you can buy a used generic tachometer on an auction web site for $15. Let us know which way you go and if you have any questions we can try to help you.