We have seen this problem before in at least one other ZB Commodore, so you’re definitely not on your own. The problem is very possibly caused by a misalignment of the micro-switch that detects the car is, indeed, in Park, and allows it to be powered down. If the computer can’t see the correct signal from this micro-switch or sensor, it assumes the car is not ready to be locked and left.

Given that yours is not the only example of this, perhaps your auto electrician has seen this before and will know what the fix is. Even if they’re not familiar with the problem, a good auto sparky should be able to sort this. If not, a transmission specialist would be your next port of call.

Many mechanics at this point would put their money on a bad earth somewhere on the car. Even though the LED light is working, the car’s computer thinks otherwise and, since LEDs draw so little current in the first place, they can be a bit hard to diagnose. Even so, the fast flashing suggests that there’s definitely a problem. To be honest, an auto electrician is probably your best bet at this stage.

Some owners of older cars have found that switching to LED headlight globes can cause the car to think that there’s a blown light somewhere as the current being drawn by the LEDs is so small compared with the normal globes the car came with. Fundamentally, the computer can’t see the current that should be being drawn when the lights are on, and fires the check-light warning symbol. You may find it’s the LED indicator light unit itself that is faulty. These can develop random failures in the internal circuitry that controls them.

The first thing to do, though, is to try the home computer reset which involves disconnecting the battery overnight and seeing if that calms the computer’s nerves. It might not work, but it’s free to try.

You need to go back to basics here. Check that the battery is connected firmly and that all the connections and low-voltage leads that power and trigger the starter motor are in their correct places and receiving power. Don’t forget to check for earth straps and cables that might have been left off in the reassembly process, too.

If the car is getting power (and the dashboard lights suggest it is) then there’s a problem between the ignition key and the starter motor. Tackle it methodically, checking for power (a test lead or multimeter will be invaluable for this) as you work your way towards the starter motor and you’ll probably find it’s something really simple and basic. Make sure the fuse or relay for the starter motor hasn’t been fried during the gearbox swap, too.