I would do the following:
1. Expose the sub's wiring terminals by removing the sub/enclosure from the rear panel of your truck leaving all the wires connected.
2. Visually check the wiring connections at the teminals and make sure they are tight, if one has wiggled loose then I think you found the problem. Upon ensuring all conections are good, check for proper sound. If nothing has changed then proceed.
3. Use a multimeter to check for voltage at the connections for the sub. If there is power present, when the system is on, and no sound from the speaker then you know the woofer is bad and needs replaced...things do get old. If there is no indication of power while the stereo is on then proceed.
4. Work your way to the amp, which is behind the interior panel in the rear on the passenger side, and check for power with the multimeter on the output side of it. This will determine if the wires might have grounded out between the amp and speaker. If there is power here check the condition of the wires going back to the speaker.
5. Check also the power in supply to the amp along with the signal wire from the headunit.
If things continue to go poorly just keep working backwards in the system until you find the problem but I think by step 5 you should have it figured out. I hope this helps...and if these steps/procedures are not anything new to you then at least I can rest assured that all that typing was for nothing.
