Is it normal for the molten brake lamp warning light to come on when the radiator fans start? I know when I start the engine the light stays on until the brake pedal is pressed which causes it to go off but on my 928 it comes on when the radiator fans are turned on when the brake pedal is pressed it goes off even If the fans keep running, then there are times when the light comes back on when the fans stop.

 

You either have a bad ground, so voltage backfeed or a bad module.

 

If power is interrupted to the bulb monitoring box it thinks you've started the car again and puts the brake warning light on until you press the peddle. It's more sensitive than most other things sharing the power so might be the only indicator. As mentioned check common ground points particularly MPV.

 

Which ground point should I check? I think I have cleaned and checked all of them. I changed the monitoring box for another one and it continues to do the same. Is it the one located under the driver's left foot support?

 

Get the wiring diagram for your year http://www.ligeti.com/928/ and look at the MPV location.

 

Valuable link, thank you very much.The ground point MP V are the ones that go above the fuse and relay box? They are all clean and tight.

 

How can I check it?