Well AllRightyThen I drove my YJ tonight with the new LED's in the engine cluster and found my Check Engine Light is dimly lit too. Doing a little research I found the light actually always has power to it but the EMC controls the flow of electricity and with a normal light bulb it * should * go out but with the LED it's enough to stay dimly lit. A samll few ohm resistor will cure the light problem.
I'm still not totally ruling out a ground in my case because the wiring under the dash it a rats nest from different radios and lights being added over the years.