Central Locking

Hello,

Long time reader of this forum, first time posting.

I have a 2004 gu cab chassis with a small central locking issue.

The passenger side does not unlock/lock by key in drivers side door or by using the switch on the drivers door.
I have removed the passenger side actuator thinking that was the problem but it appears to works fine.
The "smart entrance" ticks as usual still.

What is the correct way to test the wires in the door?
I cannot get a reading over 3v which makes me believe there is a short somewhere but also can't seem to find if the actuator needs an earth or is it only the two wires... therefore I'm not sure if i am testing correctly.