It's located under the dash where the blower id located.
I also have a 2000 jeep wrangler. This year has a problem with the heater core plugging up. You can either try to flush it out, or just replace the heater core.
The heater inlet hose on a 1999 Jeep Wrangler 4.0L is located in the left, rear of the engine compartment. It connects directly to the heater core which circulates heat throughout the cabin.
Heater core needs flushed.
Leaking heater core
Yes. It has a heater core in the dash that has air blown over it to heat the passenger compartment.
free diagram step by step at www.jeep4x4center.com
Right in front of the battery.
If your talking about the plug for the block heater, it's located in front of the battery.
Heater works fine in my Wrangler! Check the thermostat or the hoses or heater core might be plugged. The thermostat is easiest ^ cheapest to change so start there.
it could be a couple of things you could have a bad thermostat or a bad heater core
the heater core has got a hole in it or your top has a hole init. If the water is green it is your heater core. if not it is your top.
The heater core is inside the hvac housing under the dash.