by pigtail harness do you mean jumpers? You solder the jumper wires from the X-connect Ready area to your MS mainboard. Here's what they recommend for the jumpers on a KA24DE.
https://www.diyautotune.com/support/...-nissan-240sx/
Here is an image where the jumpers are soldered on the underside of the adapter board. This is a generic pic and won't match your application but you get the idea. all the J88 board does is allow you to plug your engine wiring harness into the MS ECU. You're connecting your wiring harness to the appropriate spot on the mainboard.
I would also recommend reaching out the DIY team for your questions, Matt Cramer is pretty active in the community and they provide excellent support for their product.
If you don't like the whole 'calling people' thing, I'd join the group on FB. Matt is pretty active there as well as a hand-full of MS gurus. Good place for asking help/advice specific to MS FWIW.
https://www.facebook.com/groups/mega...74474705973121