Car won't start without banging trans tun...

I've got an Australian 95 model EF Falcon GLI 6 cylinder manual and I'm now having troubles with it starting. Sometimes it will start OK but other times it needs a bang on the handbrake or on the drivers side of the transmission tunnel just below the centre console with the key held in the start position, other times I can't get it started at all. I have done a little online research and I think it's a problem with the smart lock module but I have rung a few places and the cheapest replacement I can find is $550 so I'd like to be sure before replacing this. The car has had a few mods done before I bought it, extractors/exhaust, intake mods and a cam. There is (when the car is running) a beeping from the dash that lasts around 30 seconds from start up which I was told is the steering wheel airbag not being recognised as the wheel had been removed at some stage. Some times when I lock the car with the push button remote the locks go down but come straight back up again, at this stage the doors can be opened but alarm will sound. Any ideas on how I can test the smartlock module to be sure thats what is wrong or other ideas would be aprecieated. I do have a multi meter to diagnose but am unsure what to look for. Cheers, Nathan