I have a 2006 Explorer V8 and when I shift into 4LO the RCS light comes on. It is not on in either 4HI or 4AUTO and can be turned off (causing light to come on) if desired. I recently installed the Neutral Tow Switch so that I can tow it behind the RV but I do not know if the RCS light in 4LO was a problem before this NTS was installed or not as I never put it in 4LO that I can remember. Has anyone had this issue or know what the problem could be?

 

this could be normal, I was once in a jeep liberty for a little bit that would shut off the traction control and stability programs in 4 low. The reasoning being that you would probably need wheels to spin and don't need/want the system intervening. I think the 2011 F-250 I rented did it as well

 

I think you are correct about it being normal. Another Explorer owner tried their 4lo and the RCS light came on also. There is nothing in the owners manual about it so it looks like it is another one of those Ford things they don't explain (probably don't know themselves).