WJ Grand Cherokee with leather heated seats, passenger side seat comes on the driver side does not.. the light is on on the dash but I have no knowledge base or the WJ what should I look for to replace?

The heater elements can fail due to a break in the element. You will have to take the seat apart and pull the seat cover off and replace the element

I have the same problem with my 1999 GC. I took the shortcut to the problem. I bought a 12 volt plug in heated seat pad. Works great!