ECU = engine contoll unit, the brain for the fuel injection/emmisions system.
ICS= idle control servo, a little motor on the Throttle Body that contolls an air passage used during warm up.
TPS/idle switch+ tell the ECU what position the butterfly in the T.B. is in. Also is a kind off on off switch for the idle position.
I can't imagine why somebody would bypass the MPI relay.
That's not good. Many 3.0 and 2.4 mitsu manufactured vehicles use a compatable relay that could be gotten at the junk yard pretty cheaply.

dave h.
'89 Raider V6 5spd;Aisin Hubs;; Gen2 LS: frt. brakes, rear coils;U.C.arms;R.trailing arms;idler arm; rear LSD axle w.disc brakes ;2 battery system for Dog's fan; relocated ECU; custom bumpers;J.Baker receiver;Conferr roofrack; t-bar crank.