I worked at FCA debugging prototype vehicle electrical issues for 10 years. This was after 30 years of flat rate tech work at both independent shops and Dealerships. Learned a bunch and became pretty proficient at it before retiring. What you are talking about could be fairly simple. Or near impossible. Depends on how new you are talking about. The last 5 years or so would be a can of worms. There’s way more to it than just running the wires. Intersection points and harness lengths can drive Can Bus crazy. Wire routing next to high amp circuits and multiple ground loops can send you for a loop. Many modules need messages with start and shut down times in a given order. Module A needs message to start before module B and so on. These are things very few in the aftermarket know much if anything about. Now when using an aftermarket controller it may not be anywhere near as sensitive. I’ve lived it. It can be frustrating and extremely time consuming. Example. You want to start the engine. The RF hub receives a signal from the FOB. The BCM and the KIN (key button) compare codes. If they match the KIN signal to the BCM is received and messages are sent to the ABS for brake pedal info. Also to the TCM for Park signal. Now the PCM looks at those and gives the OK to crank. The ECM looks for TAC (throttle) crank, cam signals. Then signals to prime the fuel pump and spin the starter. If the PCM sees everything correct it’ll send injector pulse and drive the coils. This is just a rough outline. There is actually many more parameters to just start and idle.
Doug