What brand MFTS do you have in there? I would only use a behr(hella/behr) brand or one from the dealer$$$ URO Meyle Vemo etc are all garbage. Even the aftermarket behr ones read a little high. The autocheck coolant warning is only triggered by the MFTS and the coolant level sensor. 2 pin sensor on the water manifold is for the after run pump and fan. The sensor in the back of the head is only for the ECU. As far as wiring goes scroll down here.
http://www.sjmautotechnik.com/trouble_s ... test_gauge New MFTS plugs are NLA I have seen some aftermarket maybe 3d printed ones available in Europe. But you can just use normal insulated female spade connectors as long as you know which wires goes where.