[slashmaster]

I'm trying to use an automotive tachometer from sun pro on the spindle. I've got 12 volts to the tach, put magnets on the spindle and am running the trigger wire through a solenoid coil with a piece of steel through it. I'm not entirely sure if the other end of the solenoid coil is supposed to go to the ground or a + 12 volts. Someone told me I may need to have a diode on it. What else can I try?

[Al_The_Man]

Not exactly sure what you have there and what you are trying to do?
What purpose is the 'Solenoid coil with a piece of steel' ?
If you want a spindle tach you could look at a automotive timing gear tooth sensor these do not require magnets to operate.
Al.

[HawkJET]

I'm trying to use an automotive tachometer from sun pro on the spindle.

What model is the Tach? It is possible that the sensing system for your tach won't work for what you are doing. The user manual should tell you how to connect it.