I was having this problem with my new (to me) 95 Defender. It was intermittently blowing the wiper fuse, quickly followed by the Code 68/stalling problem. Every time the wiper fuse blew, the tachometer would stop working as well.
In my case, the problem was an almost-but-not-quite broken wire (green) leading to the tachometer itself. Once I repaired this, the problem went away completely.
Posting here in case it helps anyone. Back to lurking.