I just recieved a used computer for my 83 NA but when I plug it in and the case touches the body it will spark like the computer has a short to the case. Does the 83 use the case to find its 12 volt ground? is this normal?
I don't quite understand what's happening with your system. But that is defiantly not normal, I have pulled my computer and laid it on the carpet and moved back to the location for it and it's never done that before.
the ecu is internally grounded. I have replaced lots of ecus just to test them (more than 10), not none of them will give a spark when their housing is grounded. It does not matter whatsoever if the battery cables are connected or not. Your ecu is shorted internally most likely.