I have NO idea, but I'd start by making sure there is power getting to the seat. Find the plug(s) under the seat and determine the wires for the heater. Turn it on and check with a volt meter to see if you are getting the needed 12V (I assume it's 12V) If not you ned to trace back along the siring.. If yes, then confirm the element is good with an ohm meter. Plug opened, put the one meter across the two leads for the element. You should get a reading of resistance. Don't know the number but there needs to be a circuit. I'd guess that either there is no power or there is no circuit. Otherwise i'm at a loss. Are there easily retrieved wiring diagrams for these trucks available? That would be the only way to trace things. And remember that the element is fed through a relay that is electronic in all probability so you won't hear it click.