I was interested to read this - it appears to confirm what I figured to be the case: that to isolate a motor, it's only the armature/commutator/ brushes that need to be isolated as they have no electrical connection with the magnet/pole pieces etc, which sounds simple on those old Triang motors. (My first post here, btw, having recently become interested in model railways after 50 odd yeas away - things have changed a bit, haven't they!)