Antilock Light & Speed Sensor

Was driving my son's 95 S10 4.3 2WD pickup this morning & the Antilock light came on briefly. I also noticed at the same time while I was rolling approx. 45 MPH that the speedo started to drop towards 0 and recovered as soon as the light went out. My immediate thought was that the speed sensor in the tranny or a connection gone bad. My son also mentioned that even when sitting still with the motor running, if he turns on the heater blower to its max sometimes the anti lock light would also come on breifly, which makes me lean towards a ground issue. Then thinking, a while back I replaced the front rotors and the wheel sensor on one side would barley touch and not clear the sensor's ring on the rotor. The plastic on the wheel sensor was already worn where it had been brushing against the ring. To allow it to clear I had filed just a slight amount of plastic off the sensor so it would clear, but not enough that the plastic broke through. My question is: If that wheel sensor is bad would it make the speedo go to 0 MPH or just give me the light?

I have only an OBD II scanner for my newer vehicles. Guess my son needs to pick up the OBD I scanner for his truck.........

Thanks,
Gene

To add insult to injury and after posting the last message, I drove the truck again to run an erron (Wife's jimmy was apart as posted on Jimmy page). Anyhow, running about 40 MPH I decided to play with the heater blower again to make the brake light and antilock light come on and this time in addition to those lights, the tranny shifted to 2nd. not only 2nd and stayed there. Even when taking off. And when rolling and lift off the gas and it coasts like its in neutral???? Crazy electrical problem? My boy's gonna be pissed lol.

Gene

Drove it this morning & it ran fine. Checked and found a code 72 (Vehicle Speed Sensor). Again played with the heater blower switching it to high trying to get things to fail again but no check engine or antilock light this time. Wondering if its might be a bad ground somewhere. Gonna have the kid remove the battery ground to chassis wire, clean and reinstall on the chassis and see if we get any changes.

Gene