Hi Padders
From what you are saying you have a reg/rec unit from the single phase charging system. The B1 charging system is 3 phase and subsequently has 3 yellow wires (one for each phase) so what you have will not work.
There is a unit available that will combine the B1 reg/rec unit which I believe you can buy from M&P and as far as I am aware is plug and play with the original wiring.
