Trying to hook a tachometer to a 93 gmc seirra 1500 350 were does the green wire go?

The "Green" wire from the tachometer should be attached to the negative side of the ignition coil only, and usually (but not always) it is a black wire with a white stripe or it is a solid white wire that will come off from the negative side of the ignition coil and often has a tab on the wire that says "Test" or "Tach" and the wire ends with an open black connector that is used for connecting a diagnostic device or tachometer for diagnostic purposes, and this is the wire that the green wire from the after-market tachometer should attach to. The "Red" wire should be attached to an "ignition" source connection on the fuse panel and have battery power when the key is in the "Run" position only, the "Yellow" or "White" wire should be connected to the "LPS" source on the fuse panel, and the "Black" wire should be connected to a good ground source and if the tachometer is not properly grounded then you will get a primary voltage shock from the ignition coil every time that you touch something metal inside of the vehicle. Let me know if you require any further assistance.