Strange OEM radio problem - it lights up when the car lights and ignition are off.

[Smells of Oil]

I have a 2002 registered Polo Classic. I've had some issues with the wiring loom and corrosion in the connectors. Took me a while to sort that, was corrosion on the connectors for the TPS (Throttle Position Sensor) and I was getting a TPS error on the diagnostic software.

That was over a month ago and the new issue I think must also be due to a wiring/connector issue somewhere. What happens and it might have been happening for some time but only noticed it with the darker winter nights is that when the ignition is turned off the radio lights come on. The radio stays off. If I switch the radio on the lights then go off but when I switch the radio back on half the time the radio waits about 5 seconds and then slowly the lights come back on (as if dimmer switch is slowly turned on).

I'm not expecting an immediate diagnosis although that would be great but suggestions as to where to look and what to check would be very helpful.

[Smells of Oil]

OK so I'll reply to myself Messed around with a few things but got to thinking that it had to be something to do with the main headlight switch? After giving the switch some abuse the lights came on but after a much longer time and not as bright? Something shorting out or tracking perhaps (metal left between the on and off part of the switch the means its part way on)? A bit more working of the switch on and off stopped the radio lighting up when it shouldn't. Its late dark cold and wet outside so I'll take a look at this again in the morning and perhaps take the switch apart or get a replacement.