The taillights in my 78 F250 were really dim even with new bulbs so I cut the back out of the housing and jammed in Truck-lite LED taillights for a trailer. I don't have any pics but they are much brighter. These are the oval shaped semi trailer LEDs and they fit perfect if you cut the back out of the housing and I used some silicone to hold them in place. The turn signals still work fine without an extra resistor or electronic flasher. I paid $32 for the taillights and wiring harness and just cut out the old socket.

 

We need pics.

 

I have a '79 F250 that I have done this to the front turn lights ...never really thought of doing it to the rears ..doh,
this is a great idea, gonna look at led for the rear too

 

I did this...