Having read this thread with interest, I would like to add some comments.
The original fuse box major flaw is mechanical rather than electrical. I mean, without even starting a discussion on torpedo fuses, and PCB routes dimensioning, the board is built around male tabs (or females, for relays) that are soldered, via their only soldering edge, to a flexible circuit, folded 180° in the middle, in an environment which is subject to strong vibration. Each tab is attached to a connector that, in turn, is also a source of vibration and movement. What can go wrong? This said, obviously the torpedo fuses and the rest of the PCB design leave a lot to be desired, too.
So, to start with, we designed each male tab of the Biturbox to be soldered through its own
two soldering edges to a 2.4mm FR4 PCB, as tough as it can get.
Regardless of the number of hours you spend soldering wires and replacing fuses, a task which is way beyond most Biturbo owner skills anyway, you can't overcome this inherent flaw of the original box.
Space is limited by the size of the box, and currents are rather high. Therefore, when we designed the board, we did it with increased thickness of the copper routes, to properly cope with the system loads - the copper thickness can be specified to the PCB maker. Same principle was applied throughout the rest of the design.
As to 50A relay, feel free to use it: we don't provide relays but there's nothing wrong with using it.
We don't have plans to make modifications to other parts of the electrical harness, except for the replacement relay with fuse, that should be available in hopefully 15 days. They are newly made, with Italamec 218 / 609 compatible pinout (i.e. direct drop in for the original fused relays), are rated 40A @13.5V DC and have a temperature range of -40/+125° C to be used under the hood.
As for current limiters, I have put a thermal switch on the heating flow regulator valve to protect its little motor if stalling, in my own 2.24v. For the windows, I trust my fingers