If you have to ask, it is probably beyond your skill set. But have you
tried taking it out and cleaning all the connections, looking for bare
or shorted wires, etc? No idea how many boards and bells and whistles
the thing has, but unless it has trip functions or something, most are
pretty simple. Wander around in the junkyard, and see if any other years
and models are interchangeable. Does it not show numbers at all, or is
the light just out? If the latter, the bulbs are usually replaceable.
The folks over in the Toyota truck groups may have better suggestions
and hints.