'06 Grand Cherokee door locks
 

I have an '06 Grand Cherokee and my door locks stopped functioning one day after my son locked the door. All of the sudden they started rapidly locking/unlocking and then just stopped. I checked the fuse and replaced it (it had blown), but this didn't solve the problem. Both the driver's and passenger's door lock switches as well as the key fob work to unlock, but I need to lock manually. I replaced the passenger locking/window controller. No luck. And checked the wiring in the doors. Nothing broken.

I asked my jeep dealer who said it was likely a broken wire and quoted me a ridiculously high hourly labour charge saying he could not advise how many hours it would take to find the 'issue'

Any suggestions?