When you start this mission you will have to make a choice between convincing God 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 God/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. When you reach the gate, Dog/God will initiate conversation.
If you are talking to Dog, he will ask to be fed, but won't give you any more clues about what to do specifically. He will also mention the Gala Event having been switched on once before.
If you are speaking to God, he will mention that Dog knows about the Gala Event having been switched on before. You can...
Force God to obey and turn on the switches.
Ask what God needs. He will ultimately has for Meat from Ghost Harvesters, and two will spawn with quest markers. Kill them for one portion of meat each and bring it back to either Dog or God.
With Intelligence 7 tell him that you can or have figured out the schematics and could walk Dog through it if God does not cooperate. God will agree to turn on the switches without any demands.
Once you have persuaded either God or Dog to wait in the switching substation, the quest is complete.
Quest stages
Stage
Status
Description
10
Get Dog to the Switching Substation in Salida del Sol.
20
Get Dog to wait in the Switching Substation.
30
Find two slabs of ghost harvester remains to convince Dog to stay in the Switching Substation.
35
[Optional] Use the Switching Station terminal to lock Dog inside and force him to do his part of the Gala.