Volvo: 1990 240DL Trunk Central Lock, central locks, actuator

Question
My trunk central lock has stopped working.  All the other central locks works fine.  I have removed and tested the actuator and it works.  I have tested for power at the connector and one wire has power when the central switch is operated but the other wire does not.  Where are these wires tied into the lock system?  Could the relay be the problem and where is it?  

Answer
Russell,
One wire is hot to open and the other is hot to unlock. So one wire has 12v the other is ground and visa-versa. Test both ways. If you have power to and ground to both during operation then lock motor has failed or become too weak to operate.