How are the light up boxes on pizza delivery cars powered?

They generally go into the lighter like this one does

Thanks Jerv. That was my original hunch. I wasn’t sure if the lighter outlet was still working when the car was off.

There is a fused “Ign” pin on most car fuse boxes usually it is 20 amps. . If the vehicle was only for that purpose you can connect the power there and keep all the wiring neat and hidden. Turn on the ignition, the light turns on. We used that pin for the instrumentation on all of our test cars.
Some cars have a fused ” ACC” pin. When the key is turned to the Accessory position that pin is powered. Not all cars have this.

Here is a sample connector that can be used for one particular car. This one plugs into the “always on” spot. They are different for other models. GM Fuse Block Tap . They are cheap. $3. ( We made our own. – Everyone had the parts in our tool boxes.) .

Cold fusion reactors.

@SecondHandStoke You are not totally out to lunch with that answer. A 16’ pizza contains about 3000 calires. If we oxidize it chemically we will get 3.5 kWhr of energy: way more than enough to power a 100 Watt light display for an 8 hour shift.
Dominos can make a fortune selling Pizza reactors.