Apparently a rig can be vehicle similar to a truck. It least that’s what I deduce from this sentence:
He collected his thermos of Coffee, a cold biscuit with ham, and a 9-millimeter automatic pistol and carried it all to an eighteen-wheel rig with unmarked doors and a ten-thousand-gallon tanker as its payload. He started the engine and checked the gauges, tires, and fuel.
Now, what is the difference between an eighteen-wheel rig and a truck?[YSaerTTEW443543]
I’d agree with that to the extent you’re talking about a regular non-modified pickup truck, as you said. However, I live in an area where there’s a lot of oil/gas production, and those who work in the fields drive heavily modified pickups with lots of additional equipment and apparatus added on to the body of the truck. These are frequently known as rigs, also.
Additionally, you’ll hear the term ‘welder’s rig’, which again is a basic pickup heavily modified with equipment such as a generator, bottled gas, and other welding paraphernalia to the extent that it’s a self-sufficient power source capable of performing the full range of welding functions from a mobile source.
It’s pretty clear that the usage does come from the idea of a bunch of stuff ‘rigged’ together.