1995 Ford Club Wagon

The ABS light comes on intermittently, once it is on, restarting the van will often reset it. It will then not come on again for, minutes, hours, or weeks.
Van has under 30K miles on it.
Braking never seems to be effected, nor is braking involved when the light comes on.
Any suggestions on what to check, or probable cause would be greatly appreciated.
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