Power Door Locks Not working

[maddoggy71]

Problem: Both door locks stopped working... the whole system is dead. Power windows work fine.

What I know:
1) The power door actuators work fine (I put 12 volts across their terminals and they lock/unlock properly.
2) There appears to be 12v at the actuator connectors, but no ground.
3) All other systems using the common ground work fine... so the common ground is ok.
4) There is no fuse problem (door locks share the main ignition system fuse).
5) The switch works properly.

I'm quite sure I have a ground problem somewhere between the main ground and the switch/actuator. Are there any common problems I should look for?