Thanks Folks.
Silyavski, in the end I didnt need resistors, as Clive says it may be because the Proximity switch has a resitor in it. Like you, I ended up wiring the Proximity sensor much closer to the BOB and it worked! :) I then traced and rewired the connections and the junction box and I'm good now. Just need to mount the proximity switches onto the frame, adjust and then see how I get on with dual homing in Mach. Thanks again.