The voltage shouldn’t be bouncing around that much during the test.
Have you checked that all connections between the alternator and battery are good?
Have you checked that all connections in the engine compartment from battery negative to chassis & engine block to chassis are good?
If you have an ohm meter, disconnect the seatbelt connector (under the seat) and measure resistance (across the connector) while you buckle and unbuckle the seatbelt. You should see it change from a low resistance to a very high resistance as you buckle and unbuckle it. If you don’t see the...
Not my daily driver so I can’t recall if there are two brake indicators, one for low fluid and the other for a failed bulb. If the latter take the bulbs out and verify the filament isn’t dangling instead of being properly connected.
Replace with OEM pressure switches. Someone on this forum tried aftermarket ones and wasted a ton of time swapping parts before ultimately going OEM. Sample size of one, but I’d spend the extra bucks to get the OEM ones.