If you need a 84 ECM, I have one you can have...Just have to find it.
I took all the electronics off the 84 before scrapping it for metal.
Let me know if you need it.
As far as the problem goes.
If you have a bad ground power will back up through things like relays and bulbs trying to find a ground source.
I would start with the grounds that will cause all kinds of havoc, are under the dash near the column.
Others are under the center console near the ECM.
Check the ground in the engine compartment near the battery.