I have a 99 F150 4x4 (5.4) 173k miles. I bought the truck from family about 6 months ago and from time to time if you stepped on the brake pedal to hard (not locking up, but pretty hard) it would feel like the passenger rear tire would lock up. He said that there was an issue with the automatic adjuster on that side. Here lately the ABS light on the dash has been coming on every couple of days, of course on the next restart it's off. Could these two issues be related?

 

Maybe, but probably not.

Please describe the conditions under which you have observed the ABS light to be on.

Does the red BRAKE light in the cluster operate? If not, it needs to be fixed. If so, does it come on with the yellow ABS light?

 

Yes the brake light works, no it does not come on with the ABS light. Most recently the light came on after I went through some water (not high but enough to splash).

 

You'll likely need to have the ABS system scanned to pull the fault code. Inexpensive scanners won't be able to do this.