Possible ground issue

This could be a ground issue, but we need to do the same test that you are doing with the test light except with a meter and find out how many amps are being used.

Basically, the radio is going to always be on so when you pull that fuse, and the test light goes out it is not unexpected.

The question would be how many amps it is drawing. It should be less than 35 milliamps (.035 amps). I attached a diagram below to show this.

As for the lighting issue, we need to start with one system and turn it on and find out where we are losing power.

https://www.2carpros.com/articles/how-to-check-wiring

I would suggest we start with the rear defogging system and find out what the issue is with the side lights on.

I attached the wiring diagram below. Basically, we need to check the power when the lights are off and then verify the power goes away when you turn them on. Then we need to trace the circuit to find out where the power is and then that will tell us what the issue is.

Thank you for your response. Since posting I've done two more investigations and think that the Aircon switch is actually working, it's just not illuminating the switches and dimming the radio/clock display when the side lights are switched on (the exterior lights are all working). so probably an internal grounding issue.

Oh. Great work. I would agree. Please let us know what happens because I am curious how it turns out.

Thanks

Good news is that it appears that I have solved the issue.,
Not 100% sure what it was but i had the kick panel off, and after prodding around a few connectors and refitting kick panel and now the radio and heater controls light up like a Christmas tree.
So, my conclusion is the I must have been a lose connector.

Yep. You are correct. I have done that many times where the connector looks and feels like it is connected properly but taking it apart and reconnecting it solves the issue.

Great job. Thanks for the update.

If the issue starts again, just try to go one connector at a time and see if you can narrow it down to one of the ones you touched. It is time-consuming but worth it when you find the one issue.

Thanks again. This info will surely help others in the future.