The 4x4 will not engage. I used the 4x4, was sweeping snow--worked fine. Then I put back into 2wd. The next day the 4x4 would not engage. Have checked fuses, and they seem to be ok. No action at all when I press the automatic 4x4 button. Are there other fuses (relay), swtiches etc. I need to check for. If so, where are the located?