The forum guys that have made harnesses include olejoedad, Timm
http://www.reddevilriver.com/, West Coast Fiero, Fieroflyer (Dan), James Brown (don't know his screen name) and Injection Technology (Phil Dull) . Some of these guys may no longer be making harnesses (or are unreliable) so check thoroughly before you buy.
I've dealt with Injection Technology, Timm and know olejoedad is a good guy but do your due diligence and check before you buy.
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" 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, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "