The modest dome light actually is wired into a complicated matrix of a half-dozen controls and switches. Doors, dimmers, thumb switches, delay timers, starter relays, locking mechanisms: all of these switches control the low-voltage interior lighting system.
Changing any of these switches will require replacement for the OEM-certified part and a detailed service manual for your specific car. Most parts and service manuals can found at your local auto parts store. If a store does not stock your part, it can be ordered.
Open the vehicle's hood and locate the battery. Disconnect the positive ("+") lead wire, which should be a thick red cable: Grip the nut that holds the cable to the battery post with the battery pliers and turn counter-clockwise until cable moves freely. Lift cable off post and set aside.
Remove the dome light lens (a clear plastic cover) according to your vehicle's service manual. This usually requires you to remove two Phillips-head screws by turning counter-clockwise with a screwdriver.
In newer vehicles, it may be necessary to remove a decorative trim or cowling. Insert a slot-head screwdriver between the cowling and the cabin ceiling. Apply gentle downward pressure and feel for any points of tension -- these are where the clips hold the cowling in place. Slide screwdriver to this point and apply more pressure until the clip snaps loose. Repeat for each pressure point.
Locate the fasteners for the switch mechanism. Usually there are two Phillips-head screws that hold the switch to the dome light assembly. Remove these screws by turning counter-clockwise. Pull the switch from the dome light assembly and allow to dangle by the wire bundle coming out of the assembly.
Remove the wire bundle attached to the dome light switch. This usually requires you to pry the plastic clips loose by inserting a slot-head screwdriver between the clip and the switch mechanism. Once the clips are loose, grip the plastic housing at base of wire bundle and pull free from the socket on the switch assembly.
Push the plastic wire bundle into the socket of the new switch mechanism. Note that you should feel the clips "click" into place. Tug gently on the plastic base of wire bundle to ensure a snug fit.
Align the holes in the switch mechanism with their relevant sockets in the dome light assembly. Replace the screws by turning clockwise with a screwdriver.
Replace the cowling or decorative trim, if necessary. Cowling or trim can be replaced by aligning clips with sockets around dome light assembly then applying upward pressure with the palm of your hand until you feel the clips "snap" into place. Repeat this procedure for each clip on trim.
Alternatively, replace screws for dome light lens by turning clockwise.
Return the red battery cable to the positive battery post. Tighten with battery pliers, then tug gently to ensure a snug fit.
