Seat belt buzzer and light won't go off

That lamp looks bright and the lens is showing heat damage. Definately on too long. Maybe a short.
I won't have a chance to look at the books until later in the week.

Your Valiant has the heavy duty wiring and back window heater grid. yes?
Maybe @townsend or @Bugman will know or be able to look into it.
Did the car have seatbelt interlock originally?
@Mattax
Thank you for your reply. Yes, it came with the optional "heavy wiring" / the 65amp Alternator.

I've looked at the pics @Bugman sent and yes, my Valiant came originally with the interlock system aswell.

I think the easiest way is to just unplug the bulb from the cluster aswell the interlock module like @moparlvr166 and @volaredon said and yeet the **** out of it.