Ok I had look and I saw what looked like a removable panel for the plug - wasn't sure so I removed the fan and felt behind and there were a couple resistor coils (one loose) and I knew that must have been it. I pulled it out and yep - one bolt+nut fell off and left connection free.

I put a new bolt with a lock nut on and it works!

Makes you wonder though - why crimp two of the connections and then bolt the third on on?

Also, the water temp sensor wire is in another harness so I wound back that emissions harness (wasn't actually connected to anything) and cable tied it behind the wiper motor - looks neater now. So once again thanks for the pointers.

Just gotta machine up a blanking plug for that unused sensor (it was used but the wires broke off so I faced it off in a lathe to clean it up.)