As the outside looked fine I decided to separate the PCBs. Luckily it's only the outside row of pins holding them together so I cut them to expose the underside of both PCBs:
Some of the solder joins looked lightly cracked so I decided to go over all of them with a soldering iron to make sure since I'm already here.
For the assembly I sadly didn't have more time nor material so I just soldered the pins back together, triple checking all of them and making sure the solder flows to the side where the cut was. If I've had more time I'd have pulled out all the cut pins and replaced them with a 1.2mm solid copper wire (which I didn't have on hand at that time)
And fully assembled:
Aaand, nothing. This time it wasn't the fuse box at fault but I'm glad I did this finally.
So upon further investigation I saw that one of the two relays located next to the ECU wasn't getting power. I pulled out some ignition schemes and found that 3 fuses located in the engine bay go towards the two relays. Checked all of them and they were good. But while playing around the fuse box I suddenly heard some clicking around the ECU. Went back in the car, ignition on and only the red light on the key pad was illuminated, after putting in the pin it went to green. At that point I knew she would start so I did not even try it.
I went back to the engine bay and pulled out the fuse box housing, at that point it was already dark and late so I didn't take more pictures except for this one:
After pulling out the fuse box itself and disconnecting the 3 plugs (in my case) that were connected to it I could see what the problem could've been. One thicker red wire looked a little bit burned leading in the connector itself.
This picture was taken from the internet, this is what the underside of the engine bay fuse box looks like:
I pulled out the wire out of the plastic and the inner crimp was a bit loose, so I pushed in the contact pins and put everything back together.
This is what the inner crimp looks like:
Couldn't find the exact one but it is really close to this one, the same type at least.
After that, assembly and voila! The car starts.
I just wanted to share this here hoping it will one day help somebody as I know the cabin fuse boxes are prone to failure.
