Good evening, and congratulations on starting your conversion. We converted our '83 to Duraspark a number of years ago and we'd never go back. But yea it was quite a bit of work. First things first: did you download and study all the documentation already available on TheRangerStation showing the various changes in the wiring harness? Secondly, have you studied the relevant electrical schematics for that portion of the engine? Most of the questions you have can be answered via either of those two sets of documentation. If you don't know how to read schematics, start with some simple examples available online, and work up to being able to read the conversion documentation. From there you'll be able to ID the wiring going into/out of "that gray rectangular plug". If nothing else, you'll be able to describe any issues in more detail. For the moment, your question is much too general to answer with any accuracy. There were a LOT of "gray rectangular plugs" involved in the conversion; we'll need more detail before any of us can give you an answer.