Random Electrical - door locks

The door locks on my 2013 2500 CC will randomly not work. The driver's always works, but sometimes the other three will not lock. Remote, drivers switch and passengers switch will always work, but may only lock the drivers door. Was a real pain on a recent three week trip.

I expect a connector is dirty or loose. Can anyone point to one/two connectors to look at?

I miss printed workshop manuals with wiring diagrams.