mup do didda.. muhfuka :salute2: 

 Your mechanic has the retardism. Connect a multimeter to the leads for each lamp, one at a time, and activate the lights to determine if one is fucky. Check for voltage and current. Filament-based lights also blow out if they're frequently exposed to drastic temperature changes, like being turned on and off, heating and cooling. This stress will eventually break the filament, which is why incandescent bulbs blow out as they're being turned on, but almost never if they're constantly on. 

 imbalance of some kind in your truck's chakras (truckras) need to use switch cleaner on bulb contacts as well as lights fuses. use a better brand bulb. otherwise consult @Rat Poster for rat eaten wires.