Electrical Issue: No lights, locks or start but airbag light illuminates

[E36X5er]

Went to start my 2004 4.4 three days ago - pressed unlock, lights flashed as normal. Interior lights were on as normal when I opened the door. Put the key in the ignition and as it began to turn over, everything went out, all lights etc… Took the key out and and tried again but it was dead. No lights, no clicks, nothing. I heard a sound when everything went out that made me think it was a short of some kind.

When I put the key in the ignition and turn it, nothing happens besides the airbag light illuminating.

Recent work done - new battery (1 month), replaced alternator with a Bosch unit (1 month)(DIY). Truck has an after market ignition after I had major issues with the factory ignition after ordering a replacement key.

Any idea if this is a fuse or relay? Door locks, hazard lights, interior and exterior lights, ignition have all stopped working