Key function of this system:
To disconnect the truck charge wire from the battery when operating dump cycle. This safeguards the truck wiring from excessive amp draw (blowing your auxiliary fuse). If your trailer is equipped with a charging indicator and/or diode (prevents trailer back feed when truck is off) I would install this on the truck side of this jibberish. The test light is not necessary but nice to show your truck is putting out voltage and that the relay is operating properly.
The most cycles I’ve dumped my trailer in a days work is 15. No Problems. If your dumping more than this I would recommend a second battery and/or some heavy battery cable straight back from your vehicle’s batteries(y).
#1. Choose a Test Light of your liking. Incandescents are nice because they show a voltage curve by brightness. LEDs are pretty but they’ll be on or off
#2. Fuse holder and fuse, 3/4 amp for relay coil
#3. Example of a nice relay and harness on Amazon:
Other Good Info on relays:
Enjoy a Charged Trailer!