If you intend to build your own harness it is a painstaking job. DarthFiero (Ryan) has been generous enough to share the wiring connections on his Sinister Performance website. Wire the connector pinouts as they are listed and everything should work out fine. If you wish to buy a pre-built plug and play swap harness Phil Dull (Injectech) seems to be the only reliable harness source right now
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "