Where is the tachometer wire located on my engine that I can splice into to put in a custom gauge?

the tach signal comes off the cranksensor and then to the module you can't tap into these wires if you are going to tap into it you will need a reluctor for the coil wire or tap into the rear of the tach on the dash.complicated

My tempo did not come with tach in the first place, would there be somewhere in the panel itself for it?

just run your tach wire to the coil to whereever it operates your new tach.