1997 Altima ABS Diagnostics

[XGamesJ6]

I'm working on a 1997 Nissan Altima, more or less a basic model, has ABS. the light has been on for the longest time. I ran a check and pulled some codes. i got 16, 26, and 57

heres the break down

16 - Stop Lamp Switch Circuit
26 - Front Left Sensor (Short-Circuit)
57 - Power Supply (Low Voltage)

I cleared the codes. and it reset and the same three came up

I checked the front left sensor, wire looked great, plug underhood was clean and secure. Couldn't remove the sensor though, took out the bolt...but thats about it.

Not sure what i can exactly check, unless one code can set other codes.

If anyone can just let me know what to check, or where to look...that would be GREAT!