Electrical issue - headlights and radio not working at same time

[bmwe30mtech]

Hi,

I have an electrical problem on my 325i. I can turn on my head unit OR headlights, but if I turn on the radio and then the lights at the same time then the radio switches off and the electric aerial retracts. Weirdly, with the radio on and lights off, if I turn the headlight switch to adjust the dashboard lights brightness, it controls the volume of the radio.

The car wiring is pretty standard and not messed around with and the stereo looks to be the original one fitted by the dealership. There is no alarm and no after market electrical items fitted or wires spliced anywhere. The only cut and soldered wires are the stereo loom to match up to the Blaupunkt tape player head unit.

Today I reconnected the wiring for the electric aerial (red to the red/yellow wire from accessory socket, white to the stereo) because it had been unplugged and a non electric aerial fitted, and it works correctly. I unplugged this again to see if the issue went away, but it didn’t so I don’t think me connecting the aerial is the cause. I also fitted speakers to the car today, but just plugged them into the original dealer fitted wiring so don’t think this caused the problem either. The car didn’t have speakers before and so I’ve never actually driven with the lights on and tried the radio, so it might have been a problem since I bought the car.

Any help would be really appreciated as I’m fairly stuck given the items work correctly in isolation from each other.

Thanks

[Contours]

If you have a charging problem, the engine management system cuts unnecessary electrical loads like the radio to save voltage and keep the car running. Lights will dim and the radio will immediately switch off as soon as you turn it on. Just a thought.

[bmwe30mtech]

Thanks, I did wonder if it was too much drawing at once, but today found the problem - the radio earth had been wired to the radio backlight wire of the E30 stereo loom. I’m surprised it still worked at all, but now fixed!

Thanks