Is your Jeep diesel, cause I don't think diesel's have 'em?
?. Mine does'nt (well not behind the bumper anyway). No idea where it is. Someone bound to post up with more info on this. Maybe worth investigating an electrical fault, and check the heater-A/C control panel.
Below is cut from the factory service manual.
HEATER AND AIR CONDITIONER CONTROL
DESCRIPTION
Both the heater-only and heater-A/C systems use a
combination of mechanical, electrical, and vacuum
controls. These controls provide the vehicle operator
with a number of setting options to help control the
climate and comfort within the vehicle. Refer to the
owner’s manual in the vehicle glove box for more
information on the features, use, and suggested operation
of these controls.
OPERATION
The heater-only or heater-A/C control panel is
located to the right of the instrument cluster on the
instrument panel. The control panel contains a rotary-
type temperature control knob, a rotary-type mode
control switch knob, and a rotary-type blower motor
speed switch knob.
The heater-only or heater-A/C control panel cannot
be repaired. If faulty or damaged, the entire unit
must be replaced. The illumination lamps are available
for service replacement.