basically you tell the game engine in the config what textures you use; after each texture you put the wound texture - all without the format suffix.
to simplify matters i quote the config of my iraqi infantry here.
this belongs to the top of the config:
#define hm_liz_iraqi_WOUNDS wounds[] = {"\IMUC_Data\liz\arm", "\IMUC_Data\liz\armD","\IMUC_Data\liz\legs","\IMUC_Data\liz\legsD", "\IMUC_Data\liz\legsl","\IMUC_Data\liz\legslD", "\IMUC_Data\liz\shirt_v", "\IMUC_Data\liz\shirt_vD", "\IMUC_Data\liz\shirt_h", "\IMUC_Data\liz\shirt_hd", "\IMUC_Data\liz\liz_l1","\IMUC_Data\liz\liz_l1D", "\IMUC_Data\des\helm_s", "\IMUC_Data\des\helmsD", "\IMUC_Data\des\helmsl1", "\IMUC_Data\des\helmsl1D"};
"\imuc_data\liz\arm" would refer to arm.pac in that folder; armD is the wound texture armD.pac, etc.
i named the textures like BIS did it (with a capitalized D as suffix, but you're not obliged to do so too. actually you can use any suffix, prefix or whatever you want)
to assign a set of wound textures to a unit you put this line in the cfgvehicle section of a unit. again the iraqi lizard camo example:
hm_liz_iraqi_WOUNDS
NB: no semicolon
you can also put the wounds[]={abcde....etc} bit in the cfgvehicle-section of a unit, but in my opinion that makes the config a bit complex.