My buddy is trying to hook up a tach on a 5.9 1st gen no computer,the engine is now in a Chevy,does anyone know how to read the engine revs.

You'll have to hook up a after market tach for that. The stock tach had a weird voltage value like 10 volt which nothing today can use. Also the only thing I knew of that you could use on that was the Dodge Optional Tach. So I would say look for a aftermarket tach designed for diesels.

where do you hook up the gauge wiring on the engine to read the rpm's?

where do you hook up the gauge wiring on the engine to read the rpm's?

1st Gens come with a computer. It's typically mounted behind the battery. The connection for the tach is typically under the dash. I've only seen one truck with the optional tach but never really look to see what wires and what colors. So if you missing the computer, crank sensor, and wiring then I'm no sure what to say...

 

This is why I suggest getting a aftermarket tach it would be much easier.