Hello Susan,

From memory.......

Mk 1, (pop up lights), I think there's a little slidey bit in the recess of the interior door handle, shows a red surface underneath when unlocked or visa versa, slide over to lock.

Mk 2, there's a rocker thingy in the door handle, again shows a red surface when unlocked.

Mk 2.5, Mk 3, Mk 3.5, don't know, could be similar to Mk 2. but may also have a master switch in the centre console or door which will lock both doors.

A lttle vague I'm afraid but hope this is of some help.