Volvo: 740 1989 partial malfunction central doorlock, rear doors, doorlock

Question
Hi,

Central doorlock on 1989 740 estate stopped working on both rear doors only at same time, both lock and unlock. front doors and 5th door are ok.

How can I trace root cause?

Thank you,

Peter

Answer
Peter,
Make sure that both lock motors work, by using a seprate power and ground. See what color wires are used and go to the relay box work the locks and see what relay is working the locks and identify that all the wires are hooked up and get power as needed when working the locks. Check the wire harness connections both sides going to the rear of the car snd see if you can trace those wires and follow the power.