My ABS light has been on and off for about 2 years. It was on for about a year and then went off as the wet winter weather arrived (good timing!). Since then, I have noticed that the light goes off when we have some wet weather (not 100% correspondence but certainly more than coincidence). When the light goes out the ABS definitely works (ie, not a bad bulb connection in addition to bad ABS).

I am guessing that the problem is a corroded connection at some place outside the passenger compartment. I have found and checked the 2 connectors on the firewall, but where else should I be looking?