Act 2: Nightfall - 7. Chap's Last Stand
*Follow the light path when in doubt.
Grab the ammo, go into the hall, but wait for the light to come on. Don't go down the hallway, instead, wait for the light to come on in the room; don't worry when he "messes" with ya. In the other hallway, wait for three Wretches. Go through, cut the dresser, and wait in the kitchen for the light to come on in the next hallway. Go up a bit then come back when you hear growling and take out the four coming Wretches. The final room has some ammo.
As soon as you exit the mansion, turn right for COG # 18.
Shoot the propane tank sitting in the car and run to it. As it slides down, you can either Roadie Run all the way, or keep pace with it and dive at the end. Go forward and meet who I suspect is Chap. Let's just call him Chap. Go behind Chap and get the ammo first. Then fill up the Junker with fuel, as Chap says.
Go to where you got the ammo to initiate the fight. Kill the five or so Drones near the steps. Then a Boomer appears near the Junker along with a couple of Drones. Kill the Boomer ASAP and then kill all the Wretches and others who swarm in (about five or so).