There is a great write-up on Mustang Evolution, with pictures, on how to replace the headlights on 1994-1998 Mustangs.
The article is located at http://www.mustangevolution.com/articles/200755/
Hope this is helpful to you.
Actually, it's located in the CCRM (constant control relay module) which is in behind the passenger front fender. It is a module with 5 relays (AC, Fuel pump, etc..). You can try to replace the relay ($10), the module used ($50-70) or buy brand new ccrm from Ford for $240. Your call. Get a wire diagram of the ccrm and replace the right relay if you go that route.
The module is located behind the headlight switch on the drivers side of the car, it is black in every model from 93-97 while the 98's have a white one with keyless entry capability, it is on a bracket against the cruise control module which is silver. so, drivers side, in the dash, behind the headlight switch, just pop out the headlight switch and you'll see it.
AnswerTurn the front wheels all the way to the right to replace the left light. There is a cover at the front of the wheel well. Remove the cover, there is a "cap" that is basically the back of the headlight. Unscrew the cap... you are at the back of the bulb. It is held in place by a metal retaining clip. Remove the retaining clip, unplug the bulb, replace the bulb, replace the retaining clip, screw the cap back on and replace the wheel well cover. The high beam lamp is replaced by opening the hexagonal cover on the top of the headlight module after the hood is raised and snaking your hand inside to twist it out and then twisting a new one in. Small hands are better!