well its been a while since I've run though any deep mud or water. I did engage it the other day when everything was wet to see how well I could power brake lolFirst off - here (attached) is the 1999 rear differential lock wiring diagram.
If the e-locker is (mechanically) functioning OK, and the only weirdness is the indicator light, my first 'suspect' would be the detection switch (illustrated on the first page of the diagram).
Did this problem begin after running through something (snow, mud, water) that could have left material on or around the e-locker? If so - I'd start by inspecting the e-locker area for crud that could be causing a short (or otherwise messed-up wiring / connections).
