Instruments dead, fuse blows immediately

[Bumper]

Hi!

I've a LHD 1999 406 D9 semi-MUX which has developed a little electrical problem after 4,5 absolutely faultless years.

I was driving around town when suddenly all my gauges and the MFD died. The car still continued to drive okay, so I just parked it. 30 minutes later the gauges were still stuck to random positions and the car was happily cranking but refused to start.
Well, I traced the problem to a blown 15A fuse on the BSI. Replacing that allowed me to get the car started again, but after a minute or so the fuse blew again, killing the gauges and MFD like before. Thankfully the car still ran so I could drive it home using the GPS for speed.

According to the user's manual the BSI fuse F is the power supply for gauges, MFD, radio, navigation and A/C. I have an aftermarket radio and manual A/C which both continued to work (thankfully) and don't have navigation. So I guess the problem is either in the BSI itself, the gauges, MFD or the wiring in between. I did check the charging voltage (which was 14.2-14.4V) as someone suggested a faulty alternator could've caused the problem.

Any ideas where to start looking? Can I just unplug the gauges or MFD and try starting the car with a new fuse or will the BSI go nuts? Any idea where to get a wiring diagram?

Thank you in advance