Bring Dog to the Switching Station in Salida del Sol South.
Find a way to get him to stay there and activate the switches.
Detailed walkthrough
When you start this mission you will have to make a choice between convincing Dog to follow you, or to use the voice clip of Elijah to turn him into Dog and taking the easy option to follow you.
Once Dog is your companion, head east from the fountain and follow the street signs that direct you to the Salida del Sol South.
Fight your way through to the switch station and here you can either lock Dog in to force him to operate the switches or you can convince Dog to perform the role.
With Intelligence 7 you will be able to rationalize with Dog. You can play the recording to turn Dog back into Dog if you cannot find ghost harvester remains. Don't turn him into Dog and he will trust you. At the switches he will agree to stay behind if you have passed the Intelligence check. Read the schematics next to the switches and tell him you'll be able to walk Dog through the procedure. He will agree.
Note: If you have less than 7 Intelligence then you can still convince Dog, although will require you to hunt two ghost harvesters for meat to stop Dog coming back. Once you have persuaded Dog to wait in the switching substation the quest is complete.
Journal entries
Stage
Status
Description
1
Get Dog to the Switching Substation in Salida del Sol.
2
Get Dog to wait in the Switching Substation.
3
(Optional) Find two slabs of ghost harvester remains to convince Dog to stay in the Switching Substation.