Here is my thinking, correct me where I go really wrong please.
1.) Lights designed to run on 3x18650 or 3x26650 should run fine on other 12V sources as 3x18650 starts at 12.6 and drops to 9.0 (or so depending on depth of discharge) so 12V would be in the nominal range the driver can handle.
2.) Car voltages are known to vacillate greatly and may be as low as 4-5V at start up (not worried about using then), 12.5 with car off ,14.5 with car on, and spikes much higher than that at seemingly random times.
Having said that my guess is that simply running a wire from the cigarette lighter to the driver would result in a working light until you started the car and it went to 14.5 Volts from the alternator kicking in, then you’d likely melt some component of the driver.
Right off the bat I gotta say, do not try this using the 12v cigarette lighter, its possible but you need to use adequate gauged wire and you need to add a relay for safety so the light can draw directly from the battery.
Another safe option would be using a set of large clamps (like on my power probe or a motorcycle battery charger or timing light) and hook straight to the battery but you seem to want the light to plug into and socket so they can carry it from truck to truck and thats simply not a good idea, some vehicles will have a dedicated lighter circuit / fuse with decent gauge wire, others will be combined with 5A of other crap, the blower motor or whatever random crap was close and that wouldnt be safe so just dont risk it. I wouldnt even put a cigarette plug on it at all so it couldn’t be plugged in by someone that didnt know better.
Are you sure the trucks your friend is wanting to use these in are 12V? 24v isnt uncommon in heavy stuff.
Assuming 12V, the best option would probably be to get a light that can accept up to 18Vin and wire it up with heavy wire and a relay and you can get a 2 prong HD plug on ebay (if you wanted it to be plug and play but you’d have to prewire the truck with one side of the coupler and a relay / other safe circuit). Using one of those buck drivers you posted will only supply up to 3A and it wont be able to do that when the car is only running at 12v since thats what it has to put out. If its claiming 1.5v overhead I’d expect atleast 2v, that means if the truck isnt charging and only idling / sitting turned off at 12v the buck converter isnt going to be able to do 3A and it’ll only be about 10v out so the light’s output is going to be pretty limited.
There are lights made to be run off of auto power so why try to reinvent the wheel? First below is incandescent bulb and the next two are LED, the last is dirt cheap. Should be easy to make or buy a cigarette lighter extension cord for one of these.
Or a rechargeable LED flashlight or spotlight such as the one below might do the job. It includes a automotive charger so in use is independent of a cord running to the vehicle. Uses built in lithium ion batteries.