Pass on right holding vehicle's first switch (6)
I believe the answer is:
Here is my best explanation:
'switch' is the definition.
'pass on right holding vehicle's first' is the subsidiary indication.
'pass on' becomes 'die' (I've seen this before).
'right' becomes 'rt'.
'holding' is an insertion indicator.
'first' says to take the initial letters.
The first letter of 'vehicle' is 'v'.
'diert' enclosing 'v' is 'divert'.
(Other definitions for divert that I've seen before include "Amuse, or turn from normal course", "Redirect; entertain", "Go out of one's way", "Turn something from its normal course", "Amuse or send another way", "Amuse or send in another direction", "Amuse or re-route", "offer entertainment", "Send in another direction, or entertain" and "Cause to change direction".)