If its definitely not the connection for the airbag underneath the front seats, the only way to diagnose the problem is to take your Puma to a reputable auto electrician. If he knows what he's doing, he should be able to trace and fix your fault relatively cheaply. Get him to give you a rough idea on cost, before you decide to go a head and book it in with him.
I've bought and sold cars part time as a hobby for the past few years now and if the car that we're trading has an airbag warning light on it is usually the connection underneath the front seats. On those problems that haven't been, we have an auto electrical that fixes the faults for us, usually at a cost of between £20 - £100, depending on the diagnosed problem.
As a LAST RESORT, and something that I obviously would not recommend for safety reasons, an auto electrician can switch off a faulty dashboard warning light. This would cure the problem of your airbag light illuminating all the time, BUT WILL NOT cure the underlining problem in the airbag electronic circuit.
