Ford Repair: 94 ford explorer abs, ford explorer 4x4, wheel sensors

Question
I recently had my front brakes done on my 94 ford explorer 4X4.  After the job was finished, my ABS light started coming on. It had never come on before.  It actually came on as I left the parking lot of the place that did my brakes.  I immediately went back and told the mechanic.  He said that there was nothing he could have done to the ABS system.  Is he right?  Somehow I suspect he did something to the ABS front wheel sensors.  
Do you have ant ideas? If so, how can I fix the problem?

Answer
If the ABS light was not on before the work, then most likely something was disturbed or moved. I hate to say damaged, however there are several things that could have happened. If they changed the rotors, there is the possibilty of using the wrong rotors, provided your vehicle has 4 wheel ABS. You probably have rear wheel ABS, in which case working on the front brakes would have nothing to do with the RABS.

There are many possibilties. I'm surprised the shop didn't at least take a look at it for you, since they just worked on the brakes. At least a check for a code to aid in knowing what part of the system is turning the light on.