Good info on this site.
For those that are new to this car but working on them....
I pulled the cover off of the harness. There are small numbers imprinted at the end of each run of wires. I counted from the end of row #25 until I found #48. I used a two wire splice for my signal to aftermarket tach. Put the wiring harness cover back on, rebound the wires in the loom and put everything back together. Fired it up and it works as promised.