It's on a 92S
Located Drivers side, next to rear seat and internal quarter panel

 

Good question! You would think its fordiagnostics but it wouldn't be unde all those panels butitmay be for checkingengine diagnostics. Orits for a power antena and you car isn't equiped w/ that. It also might havesomethingto do withthe electronically controled 4 wheel steermodels. I'll check my Si and post back