The light on the dash that shows your in 4WD isn't working. I pulled the plug off the sending unit on top of the transfer case and used a jumper wire between the 2 terminals. The light came on. I'm "assuming" it's a bad sending unit. If the transfer case were low on oil would that keep the sender from working?...The 34P shows part number 15594176. NAPA doesn't show that but shows a FWD37. Is that a good cross?