I saw one guy on a 67-72 truck that added a couple of super bright red LEDS to his cargo light. Just drill out the cargo light bas to mount the LEDS.
During the day it looked just like every other cargo light, didn't notice the RED LEDs in it at all. But when he hit the brakes, those 2 LEDS were almost blinding.
That's what I'll be doing if I ever do that mod.