A wiring diagram makes trouble shooting a circuit a much easier process. By knowing exactly what components are serviced by a circuit, can greatly reduce the trouble shooting time. Individual components can be disconnected and temporary jumper wires can be added to effect a working circuit. Once a fault is localised, it can be isolated and replaced/repaired.

A wiring diagram can't repair a short, but can be an aid in determining where the fault is located. Unfortunately many after market conversion companies cannot or don't supply accurate wiring prints. It seems that many installers run the many ordered options, in a way that best suits their needs at the time of installation. I would think that a trailer manufacturer that installs its own interior, would have a better method of placement regularity, and would know exactly what is connected to what, and where it is located.

You have to determine what is serviced by the troublesome circuit. Then you have to determine which component is causing the problem. If several components show to be a single cause, usually it is the wiring to them that is the complication. Starting at the end of the circuit and working towards the power source, will be the easiest way to determine and isolate a fault.