[xtrememeasures]

why would u need a voltmeter that reads past 1000 volts when tach should be between 1 and 6 volts AC..so make sure ur voltemeter is on alternating current and test the wire....at rest it shouldn't read anything then while running it should read between 1-6 volts AC....like orang said its a white wire that could be connected at the coil or i think its also at the black plug on the ecm..u don't have to drill through the firewall just poke like and anteena throuhga rubber grommet and feed the wore through that way

 

[xtrememeasures]

10 pin at the gauges inside the truck??

 

[xtrememeasures]

don't count the pins ..like i said its white and i belive it in the black plug.....if not u can grad it at the ignition coil or any of the injectors...if u grab the tach signal from an injector look at all of them ...each injector will have one wire on all of them that is the same color...tap into the one that is an opposite color