Have a 2009 Hummer, was manufactured in Africa.
Security lock icon appears after starting vehicle stays on. Had diagnostic tests, unable to enter car security system to clear fault, faults with Radio lights and AC unit plus doors able to clear these only for them to return again. Battery being drained by something while the car is turned off. If left sitting for 2 /3 days the battery is dead. Anyone out there has any advice would be much appreciated from Sydney Australia, cheers

 

sounds like you need to take a look at your BCM harness for corrosion.

 

Welcome to HF.

1) if you are still using the OEM Crappy Azzed Battery Terminal Connectors, hack them off and replace with a quality aftermarket set like Stingers or your favorite brand.
2) look at the wiring harness with the rear door open between the bumper and chassis to the license plate light, many rub on the chassis and wear out the insulation creating a short. That killed my battery 2-3 times until I found it, same with quite a few more H3s over here.

If that does not help, do a parasitic draw test.

 

Thanks for the info guys, I'll look at all of these and let you know how I go