Sprinter 311cdi tachograph fuse location? ?

Hi everyone,
I have a 2004 Sprinter 311cdi that used to be a wheelchair minibus. It was converted by UV Modular. There's a tacho fitted that I don't need or use as I've turned the van into a campervan. The other day I changed the stereo and in the process seemed to have blown a fuse, there's now no power to the stereo or the tacho.
I can't find the fuse anywhere. Underneath the steering wheel are the standard fuses, but the one marked "stereo" is fine. The small fuse in the stereo is also fine. I've looked under the driver's seat and there's no fuses that I can see, just lots of relays.
The secondary systems installed by UV Modular have a fuse board with LEDs on, but none of those are lit up either.

Can anyone help??