I know why the ABS light is on.
So I was trying to find out why the scanner I just bought wouldn't pull ABS codes. Online I came across a video of a guy diagnosing ABS issues on a truck like ours. Turns out no scanners can pull ABS off these vehicles. But then he showed the most common reason the ABS lights up: a sensor connection on the master cylinder. Checked ours, pulled the plug out and one of the pins is obviously broken. "Well there's your problem!" So I need to replace that connection.