Noticed last time I drove the Polo 1.9TDI Classic that the ABS light came on with ignition and went 'out' after the usual couple of seconds in the normal way but after the engine was started and all the other lights had gone out the ABS symbol was still faintly visible. On switching off after the drive the ABS symbol was still faintly visible after I was out of the car and had locked up. On checking it is faintly on all the time, quite obvious when parked up in the dark and just barely visible in daylight. VCDS scan shows no brake/ABS faults. I know electrics on ageing Vag cars can be a problem. I don't drive it more than once every couple of months as I have a Bora as a daily. It's more of a family emergency car as it has been so reliable in the past. Battery does run down over a month or so. Anyone got any ideas what to look for?

That seems more like a problem with the speedo unit, you might find removing the connectors from the speedo and give them a spray with some contact cleaner might cure it or it might be a dry joint on the PCB connector inside the speedo 

Been using the polo as my daily driver while I try to unlock a stuck rear door on the Bora. So a week of several drives a day, heater and ventilation on, the car seems drier and today the ABS light went out normaly and didn't glow faintly. So must have been a tiny current leak due to the damp. Although it didn't seem very damp but it does have a sunroof. So, sorted itself.