I just did this today on my 1996 Tacoma 2WD, don't know if it's the same for 1999 though.
Four Philips-head screws hold the taillight assembly to the body. Remove them obviously. Separate the...
Answered in another forum which was specific to Tacoma models 2005 and later.
"I have the same issue - Found a picture of a replacement taillight assembly and the assembly is held in by more than 2...
to remove tail light's. open the tail gate. remove the 2 10mm bolts with out washers on each side..then you must pull the light straight back....it will be tight but their are no more bolts holding...