That is not a ground wire. That wire provides power to the junction box on the left side of the engine compartment. If it's broken a lot of stuff won't work. It must have been hanging on by a few of strands of copper wire, hence the weird behavior, and broke completely when you removed it. You wouldn't be able to start the car with it completely broken or disconnected.

Take heart! It's an easy fix.

Edit:

As I read your post again, "...when pulling on the big blue wire hidden under the battery it offered no resistance. It came out completely and cleanly broken off from it's terminal," makes it sound as if this was not connected at all. That sucker is always hot and you don't want it just lounging around like that.

Was there another wire of approximately the same gauge from the + battery terminal to the j-box? Maybe some jack leg fix by a previous owner or mechanic?


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'79 242, '84 DL 2 door, '80 DL 2 door, '89 DL Wagon, '15 XC70 T6 AWD