I have a Merc 320ML 2001 which has fault lights on BAS, ESP & ABS - any idea's on the fault would be great?

I think on an 01 ML the ESP control unit is still inside the electrical box under the hood. There was never a problem with them there. However the ABS unit connector is located under the windshield washer fluid reservoir where the fluid can spill onto it. Check the connector there. PS has the brake light switch being replaced yet? Hate to say it, there's are some scum bags out there that will tell you its an ABS unit (which is very rare), when its a cheap brake light switch (which is very common)