I, too, was fighting a JLG 2630S issue with the Pothole Switches. Thankfully I found this forum thread and saw the recommendation to enter the Machine Setup area (I needed to enter the Level 2 access code first to be able to make changes) and set the Proximity Switch from "0" to "1" and it completely fixed the issue. THANKS!
The 3121166 manual sure doesn't do a good job on this; the wiring diagram showed the switches in series, but the Section 6 Diagnostic Trouble Code chart for error 256 (page 6-9) clearly infers that is NOT the case, stating the Left switch connects to J1-9 and J1-10, with the right connecting to J1-17 and 18.