Welcome to Just Commodores, a site specifically designed for all people who share the same passion as yourself.
My mate had this exact problem not too long ago, after 2 mechanics and countless posts on these forums we decided to get it towed to a holden dealer who then identified the problem as a faulty body control module caused by a water leak.
if you have tried all the basic trouble shooting like relays fuses checking wiring etc, might be worth going to your local wrecker and seeing if you can get a loan of a ECU and BCM to test if thats the problem.