Worst thing I ever come across is custom and aftermarket wiring.
It's all good for the guy who strung it all together and made it work, but even the slightest bit of troubleshooting becomes a total nightmare.
WIRING don't get me started! I worked for a dealer and had to deal with custom conversion vans, once I had a major problem with interior lighting, pulled part of the headliner down to find all blue wires about 20 of them? Pulled down the rear of the head liner and found about 10 white wires? Ripped out the whole headliner and they ran leftover blue wires that were to short and added white wires to then in the middle of the van! These were new factory conversion vans. I had another van that someone ran the screws to hold up the headliner right through the roof, had about 25 screws sticking out of the top, man we laughed our *** off.