I have breifly looked into my 02 EB seat heaters as both driver and passenger seats fail to warm even thought the indicator lights up on the switch. When I dismantled the passenger seat and put 12V to the heating element, it worked very well but on the driver side it has an open circuit (break in heating element) and would not heat. I plan to replace the driver's side with an aftermarket system. The passenger side however, may be a bad heated seat module or the temperature sensor wire embedded alongside the element which sends the signal back to the module to regulate the temperature.
The aftermarket system I was looking at is approx. $200 and it comes complete with seat bottom and backrest elements, module and 2 setting temp switch. I have to look into it a little further but as the weather is warming I suspect it will not be until nearer the fall.
I have purchased a FoMoCo 2001 Expedition/Navigatoe Wiring Diagram Module and hope to put it to good use. | 
