The most likely issue in the wiring is at the connectors or a wrong spiral, so check that first. You'll want some small safety pins for back-probing connectors and for simulating male pins. Your aftermarket spiral may not have the same wire colors as the original, if it doesn't then you'll need to look for the proper pattern instead of going by the wire colors. Slight PITA, but that's always an issue with aftermarket electrical parts. Assuming the colors match, with the airbag and brain loose but the spiral connector M29 still in place, poke one safety pin into the airbag connection White wire and another into the back of M29 at Yellow/Blue. You should have continuity. Then do the same for Green to Yellow/Black, Red to Yellow, and Brown to Yellow/Black (notice the two Yellow/Black wires should be common, they join inside the harness). If you find anything that's open-circuit then your spiral is scrambled and isn't the correct part. If you don't find any opens, then take M29 loose from the spiral and ohm the wires between M29 and the bag brain M35. Same deal, all should have continuity. If any are open, then the problem is in your Main Harness and you'll probably be best off cutting the open conductor at both ends and splicing in a parallel wire. If you don't find anything open, then you have a pin-fit or corrosion problem in M35 or one or both bag connectors.
One word of caution, get a safety pin
assortment and never force an oversized pin into a receptacle, you can permanently damage the receptacle spring. At least three quarters of the pins on any Nissan are 0.025" nominal diameter, so you can use a calipers to find one made with 0.024~0.026" wire and use it as a spread terminal pin-fit checker. If it drags in the cavity, then the receptacle spring is good. No drag, it's a loose pin-fit.