Vacuum and power boost are unrelated to the ABS and won't turn the ABS light on. If the ABS light is on, it's more likely the ABS valve in the rear brake line, or the module or the like. Does the speedometer work normally?
Does it seem to come on say after a hard turn, or like a banked on/off ramp? My fluid level was fine but I got on the highway on a fairly banked on ramp and was pretty deep into the throttle with 10,000 lbs of fiver hooked on trying to merge into traffic. Drove all the way to Yuba city with the light on. Stopped at a rest stop, shut the truck off and when I restarted, no light. When we got home, I experimented and pushed and held the float to the bottom, and when I turned the key to the run position my ABS light would come on.
Not saying that's your issue, but my float seemed to stick, and once I got it moving freely, haven't had that light again, been at least 2 years now.
1994 F-350 7.3 IDI Turbo, crew cab, E4OD,4:10 L/S, LB, Dually Photos
ATS Turbo upgrades: 3" DP with 3" exhaust Magnaflow XL muffler: Pictures Here
2012 Copper Canyon 273 FWRET w/2 slides, Air Lift 5000 bags
Pillar pod: Autometer C2 Series gauges: pyro,trans, boost, water, oil pressure
Hypermax Cowl induction, K&N air filter, flex-a-lite 26K trans cooler with fan,Tekonsha prodigy
Train Horns: Pictures here