I dont think Scamp
ever used a junction box, although its a good idea and I added one. I put mine under the front seat but most people put them on the tongue (outside).
Start with the Scamp wiring diagram
and use your multi meter to check voltages and continuities to verify everything. Dont assume by color alone. Probably will want a helper to make connections, turn things on and off, etc. Just don't burn out your meter on the continuity (Ohms) settings. If you don't know what that means then I suggest finding someone with some low voltage electrical
and wiring knowledge to help with this in person.
Photo is my umbilical cord with junction box, mixed in with my solar
and Trimetric stuff.