Sam White

Likelihood if all the switches are good and the gauges are showing the correct pressure you have a wiring issue. The 'healthy' signal is not getting back to the dash. It's a case of getting out a multimeter and perhaps an extra bit of wire to help with the long loom run back to the cab to identify the culprit. Also by identifying the 2 contacts that are not talking, yiu can pull a new cable point to point rather than trace an old loom for damage, likely causing more problems to fix!