this is the wire you use for runnning an aftermarket tachometer or adding a an SR5 cluster with tach to a standard model vehicle
In the engine compartment, you will find a green wiring plug that runs off of the negative side of your ignition coil. You will need to run a wire from this plug, you run a spade plug from this connector to the tach, or sr5 cluster through the firewall, into the blue connector that plugs into the back of the guage cluster. The blue connector is know as "Connector A" in the factory service manuals. There should be 12 slots in the connector - A group of 5 slots on one side, and a group of 7 on the other. There will be a little plastic divider between the group of 5 and 7 slots. Count over to the sixth slot (through the group of five, and then the very next slot is the sixth.), this is where the wire from the ignition coil plug plugs in. That will get your tach to work.