Airbag Fault - Flashing Light

[Macross]

Having some issues with my r34 gtr.. had it in a shop a while ago for some work, as far as I know, they needed to remove the passenger seat, glovebox compartment and potentially the centre console, the battery was disconnected for a few days as well. Picked up the car and was told the airbag light was flashing, consult system couldn't connect to ecu to do anything about it (normal as far as I could tell as the car has a powerfc), rather than leaving my car there (first time I had used the shop) I took delivery of the car and left it for a while as I would rather take a look into it myself than let them muck about with it anymore.

Now it's a few months later and I've finally found some time to look into the problem, but it's already shaping up to be a messy one from what I can tell. Started with the manual reset (pressing the door switch), the light however doesn't stop flashing but I can hear what I think is the system pressurising (this sound only appears after I do the manual reset and not othertimes) when I turn the ignition off then on again. Tried this several times on several different occasions, all with the same results. Switched to next step, borrowed a stock ecu and installed it in the car, tried manual reset again with no luck.

Now I'm concerned because something could have been damaged when the work was done and I have no idea what it could be without going through the whole system.

I'm going to see if the bridge over the fusebox is getting power to start off with, but besides pulling out the workshop manual, ripping the interior out and manually tracing the wiring along to see any obvious faults, I'm wondering if anyone has some ideas of any plugs/important items that may be located around the passenger compartment that I could start by checking?