'85-'86 models: Remove the plastic panel on the lower left side of the dashboard. Remove the screws that attach the fuse box, then pull the fuse box away from the dash. Dig around amongst the wires behind and above the fuse box until you find a blue connector plugged into another connector. There should be a green connector nearby that's just like the blue one, except that it isn't connected to anything. Disconnect the blue connector and plug in the green one where you disconnected the blue one. Install the fuse box and plastic panel.
The procedure itself makes decent sense - but the part I'm not clear on is what happens after the blue connector is plugged into the green connector. Do I just leave them plugged together, or do I return the blue connector to the one it was originally plugged into?
Testing showed that the EGR valve is actually shot, and the new one should be here in the next day or two; it'd just be nice to know if after moving the connectors around the light is permanently disabled or not. If it's on a timer I don't really care if it's gone for good, but if it can actually detect an EGR fault I'd like to have it working at least while the new one is bedding in in case something goes haywire.