Central lock of tailgate

[BoBoKwok]

2001XC
the central lock of the tailgate stop working
The lock doesn't lock both by key and remote control.
However, it can be unlocked.
I've checked that all linkages are good. The problem is that the actuator can pull only but not push.
Then I took the actuator out. Disconnect all the linkages and tried again. Still not pushing
I disconnect the connector. There are 4 wires. 2 for the actuator and 2 for the tailgate relay.
I measured the wires to actuator with a multimeter.
No voltage
I push the unlock button of remote. 12V measured
I push the lock button. No voltage
I took the actuator home and applied ~6V to it. It push well. Then I reverse the polarity. It pull.
I believed that the actuator is good.
Problem is electricity to the actuator doesn't reverse so that it work only in one direction.
Anyone can help telling me how to fix it?
Thanks in advance

[Willy]

It may be a wiring problem:
http://www.volvoxc.com/forums/showthread.php?t=10782&highlight=tailgate+wiring
Willy

[Aviator]

As Willy said, most definitely a wiring problem most likely at the gate hinge harness/es.

Dave.

[BoBoKwok]

Let me check the wiring tomorrow.
Thanks guys

[BoBoKwok]

I inspected the wires inside the hinge. Their appearance are fine. No crack were found.
During the inspection, I suddenly remember that there are only 2 wires to the actuator and I did measure voltage so that wire should not be the problem.
What and where is the module to send signal to the actuator?