how do you install a tachometer?

[BIGCRIP28]

I bought a universal tach on ebay and im not familiar with installing them.
First off it is going in a S10 truck. The tach has 4 wires coming out the back: red, black, yellow, and green.
Im guessing green is for ground and red is for power. Anyone know which colors go to what?
Where is the wire usually that you hook up to? Im guessing behing the dash.
Can anyone give me any good advice?

thanks in advance.

[250rAL]

Not positive but... the red and black should be power and ground,the yellow is probably for a light and the green is for the RPM's. On older cars the green would go to the coil; I don't know where they go with them now.

[84honda 200X]

For my dad and I's 56 dodge we have a tach in it because we have a built 350 chev in it and all the wires run under the dash and are conected to a jack and you stick the jack in the tachometer. But yours sounds way different then ours.

[bigb9582]

red is power, black is gound, yellow is aux power (power that comes on with the key), green is the rpm signal which goes to the negative side of the coil but if its a newer truck with the distribiterless(sp?) ignition system, you will have to get a wiring diagram for your truck to find the rpm signal wire.
edit- thats how mine hooks up but yours can also be red is aux and yellow is for the light. depending on if yours has a programable shift light, if it does go with the first one i said, if not go with the second.