It is rare that both motor relays would burn out at the same time. If both do not go up its usually the headlight switch or isolation relay. You say you replaced them but no change. Are you sure that isolation relay was good???? If so I'll take a long short guess and say that its the motors themselves.
Some detailed repair info from engineer and long time Fiero owner Oliver Scholz here:Gen 1 Headlight motor repair guide
------------------ " 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 "
[This message has been edited by Dennis LaGrua (edited 05-16-2020).]