so I pulled the G-56 out of my 06, and I've been driving it for about 2 weeks now with out the front drive shaft, and all of a sudden the service 4Wd light comes on, is there a sensor in the transfer case, that would make it go on, I'm going to put the front drive shaft on again for sure, just curious I guess

 

Check the connector on the shift actuator (I'm assuming it's an electric shift t-case). make sure it's fully seated, sometimes you need a bit of dielectric grease to help the seal slide until the clip locks into place, Being as it was recently out, if the clip didn't lock then it may have backed out a bit. Less common but I've also seen loose pins where the sifter would only work if you pushed the connector off to the side a bit, in which case you would be looking to replace the connector. a front drive shaft makes no difference, there are no speed sensors for it.