excuse me if this has been covered,,my dieing computer is not gonna give me time to read thru this thread.

I've had a main relay get all green and corroded on the inside. It containes 2 relays inside. They contoll fuel pump and switch vacuum line switches for charcoal/vapor , egr and such.
When mine went I thought it was ECU 'cause that's how the code read. There is no code for Relay itself.
Junk inside that relay could cause intemntant failure so I wouldn't totally trust the "bench test" for the relay without popping the cover off it to look for corrosion.
If you find a junk yard 3.0 Diamante and Sigma donor, etc,,,the relay with be the same.
Also possible dead internal distrib modual, but that should give cam or crank sensor code.

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.