Myford Tri-Leva lath

[AdieB]

Hi all had a call from an OAP who has a small Myford Tri-Leva lath single phase in his shed. All was working ok off a plug top then a friend suggested fitting a rotary switch which would give both forward and reverse on the lath. Friend connected it up for him and now it just trips the rcbo when switched on. Friend has disappeared. There are 4 cables that come out the motor two reds and two blacks. One red goes to a terminal marked AZ , one red goes to a Terminal marked Z, one Black goes to Terminal marked A and the other black goes to a terminal that is not marked. To reverse the motor rotation it says to swap the AZ and Z internal motor cables. So those terminals must be the switch wires for forward and reverse. But are the black cables a neutral for either. Just thought should have put ohm meter across pairs to see if there was a coil resistance between. Has anybody worked on a lath like this or know or have connection diagram would be appreciated.