1996 Ford Expedition ABS brake light.

I have a 1996 Ford Expedition Eddie Brower 4x4 with approx. 115K miles. It has the towing package on it as well and I tow my 2 horse trailer with it. While driving today (without towing my trailor) the "ABS" light on the dash came on. When you turn off the vehicle and re start it the light comes on for a minute then goes off. When driving it comes back on again. I have never had this happen before. I towed my horse trailor yesterday and it was raining. Someone said I could have water/moisture in the connector plug causing the light to come on? Could pulling a trailor case this light to come on or was it a coincidence and be another reason and what else could cause it to come on? Thank you.