Does anyone know what size is the reverse up light bulb size? Cree bulb size. An Cree third brake light size?

 

Reverse Light is a 3156. I use Cree for all of my exterior bulbs. I don't know what it would be for a factory high mount brake light since the one on my truck was an aftermarket piece installed by the previous owner. I think it would be a 194 though. If you search my posts you'll see that I upgraded my rear brake lights to all Cree LEDs. Be sure to get the 7W Q5 if you can. Cree has recently come out with a newer 10W which I will be installing at a later date.