With patience it can be done, the first thing is \ "stamping the cables \", that is, on the car investigate how you well say what each of the cables that it carries and with the help of a notebook will be used to write down everything eg:
black-yellow position and lighting
green frame-blue intermittences
White witness long lights
once made the letter with the cables, it is time to make the opposite part in the box cables to the chips and as you have said with a 12V DC source to feed cable cable in the chips to check what each cable does.
With these two lists, what you have to do is link the car to the painting, and make sure that the order of the cables is what you want.
Thus I adapted the picture of an Opel Kadett F GSI with a digital picture to a corsita A from 86, and when you put the contact and see all the digits that go up and then they are placed, you forget all the headaches that bring the fucking cables.
Greetings and hopefully everything goes well.