What's the legal way to use a baby car seat in a pick up with only one seat?

Other answer:

You install the child seat exactly like you would in the rear seat if you had one, then (and this is important) you disable the passenger side airbag. Don't listen to the answer telling you to turn a rear-facing seat around, that's totally wrong.

Yes there is a way to disable the passenger airbag, it's required by law everywhere in the civilized world. Find the switch (look in the manual if needed) and activate it.

Poof… you're now doing it legally.

It's usually legal to place a baby seat in the passenger seat of a 2 seat vehicle. Not quite as safe as a rear seat, but you don't have that option.

If you can't turn off the passenger air bag, then install the seat forward facing. Again not quite as safe as rear facing, but its the best you can do, and legal. DO NOT install a rear facing seat if you have active air bags, If they go off, the baby and seat will get catapulted into the back of the cab (Not good).

Rear-facing seats should never be in the front seat if the airbag is on.
Yes it is legal & perfectly safe. Single cab trucks (and most extended cab trucks) have the ability to turn the air bag off.

Our extended cab truck has LATCH on the front seat with a switch (key required) to turn the airbag off. We've never installed a seat up front, but if we had to (too many kids in the truck), we would.

If there's no back seat, how can a child sit in the back seat?

If you only have one seat, who's gonna drive?

I know, just having fun! You use the infant seat just as you would in a car. I would use the middle seat position if it were me. That would better isolate from a side impact.

A thought shared.
Bad Speller:
not legal
don't use it