I disabled the seat belt alarm in both of my mustangs. I did it because lots of times I like to sit out in my car during lunch and listen to the radio.
It may or may not be the same for your truck, but here is how I did it
1) Turn the ignition switch to the RUN (or ON) position. (DO NOT START THE ENGINE).
2) Wait until the safety belt warning light turns off. (App. 1-2min)
a. Steps 3-5 must be completed within 60 seconds or the procedure will have to be repeated.
3) Buckle then unbuckle the safety belt three times, ending w/ the safety belt unbuckled. This can be done before or during the Belt Minder warning activation
4) Turn on the parklamps/headlamps, turn off the parklamps/headlamps.
5) Buckle then unbuckle the safety belt three times, ending with the safety belt unbuckled.
a. After step 5 the safety belt warning light will be turned on for three seconds.
6) Within seven seconds of the safety belt warning light turning off, buckle then unbuckle the safety belt.
a. This will disable Belt Minder if it is currently enabled, or enable Belt Minder if it is currently disabled.
7) Confirmation of disabling Belt Minder is provided by flashing the safety belt warning light four times per second for three seconds.
Confirmation of enabling Belt Minder is provided by flashing the safety belt warning light four times per second for three seconds, followed by three seconds with the safety belt warning light off, then followed by flashing the safety belt warning light four times per second for three seconds again.
9) After receiving confirmation the deactivation/activation procedure is complete.
__________________