In our 1993 U240, remove the fiberglass cover on the inside of the Tail Light fixtures (in the engine compartment). Squarehead #2 screws hold the cover in place if I recall properly.
And while in there remove and wipe the dust off all the other bulbs as well. Brett Wolfe 1993 U240
I have a 93 GV and Brett is correct. However, on my GV there was a large amount of caulk around the enclosure so it was very hard to remove. I thought it was not the method to access the taillights. I finally pried the enclosure off and Hooray, I was able to change bulbs.
The caulk they used helps keep dust out of the tail light so when I replaced the cover, I put a new, very small bead of caulk around the cover where I could reach. Unless the original installer was the size of a packrat, I don’t know how they got in the compartment to caulk the entire cover. I suspect it was done before the rear cap was installed. Kent Speers 1993 U300 40′