This appears to be a common fault with VS Commodores.
I have fixed two of these at no cost.
The fault lies in the turn signal/high beam switch.
To repair...
Lower the adjustable steering column, remove the upper & lower steering column plastic covers & remove the turn indicator assy by manipulating the tangs.
Unplug the two wiring connectors & you have the turn signal assy in your hand.
Utilising very small screwdrivers or scribers or whatever suits, lever open the retaining clips & separate the two halves of the switch very carefully, noticing where the springs & 3 flat plates came from.
You need to bend the largest plate SLIGHTLY in the middle (maybe 5 degrees) to adjust the distance between the plate contacts & the high beam contacts.
I'm sorry that I can't be more specific about which direction to bend it but you'll have to sus it out as I did.
The fault seems to arise from one half of the plastic housing lifting slightly under spring pressure & allowing the high beam contacts to be too close together when they should be at rest in low beam position.
Typically the high beam comes on or flashes on its own & low beam can only be selected by holding the turn indicator stalk in a certain way.
The alternative of course is to buy a new turn signal assy.
I wouldn't recommend buying a second hand unit from the wreckers as it may have the same fault or soon will.
If you've had the headlights on & noticed the high beam flash momentarily as the turn signal indicator cancels then that is another sign that the turn signal switch is nearing the end of its life unless you do the abovementioned fix.
Cheers