If anyone wants to buy a ready to run harness, they can contact Rob.
His harness for FSJ's is shown here.
However I think the question is about who to contact for fixing Serehill's harness, which is different design tthan Rob makes or Mass is intending to make. Partspickup, if that's your question, I think the answer is we'll have to solve it here on the forum. Rick's son was intending to followup on the making and selling harnesses, but for whatever reason has not done so. In fact I sent him the one I purchased so he'd have a model.
So if its a tech question, probably just start a thread in the FSJ tech fourm. When you do, please mention at least the year of your SJ, as the wiring went through a few changes, the biggest one probably in '86. In the meantime I'll look how Rick wired his harness, but from memory your theory its the relay seems reasobable.