Thanks @THE RADMAN , I will need a lot of it, the weather, work and baby dont help .

@haz87 , the raison for the fuse box in the first place was the fact that half of the contact where corroded and I think one on them was completely rusted away.
For the light, nothing was wrong in the first place, that was the central locking wire the issue. Somehow one of the wires got the insulation cut and the coper inside started to oxidise, and at some point, it started stop being a wire depending on how hard I was slamming the door. That what started the "letch make my own wiring" and because I'm working with ECU, CAN and electronic/embedded system in general I decided to modernise the car.

To start, I plan to have the car working as it was before, with the original dash, and a “custom switch panel” for the light, fog light, wipers, etc … as the wiring is a mess one the comodo, I couldn’t figure out the indicators (haven’t tried hard enough but they will be changed later). The engine management stay the same and hopefully I get an MOT.

Next that will be adding prox key, remote start (should be easy as I already connected the necessary wire to start the engine without the main loom, just need to replace the ignition barrel with a couple of relay and I can start the car electronically with a microcontroller), and CRT for the infotainment/dashboard like the 1986 Buick Riviera (why ? because that look awesome). I’m not sure how the CRT will survive the vibration as the will be from old oscilloscope (dead part from Ebay) and not really design to be on the road.

I also want to change the engine ECU and add a compressor to the mix. The injection system is really old, it has to inject 3 time to get the correct amount of fuel because the ECU only have injector driver that drive 3 injectors at the same time.
No tuning capability out of the box, I probably have to change the eprom or rom in the ECC IV if I want to do that.