[alsriv2]

I might need a small correction here, but I do believe that each LED diode only takes .7 volts to fire up and produce light (sometimes less).
mmiddle is correct about the random stray voltages that our trucks typically have and the need for an inline resistor "load equalizer" to be placed in line prior to the LED lamps for them to function correctly.
Higher quality automotive LED light systems will typically have the required resistance built into their product, others will require the new owner to calculate the needed load and install it themselves.