Diff lock light flashing, interaxle light on, is that correct?

On my I believe the Interwheel light flashes ( two wheels with x in middle) with interaxle off. While running. Normal?

 

Oh! Nope. I think I had this happen in one of the volvos I had, though. I had that rear chassis harness replaced a few times in the million miles I had that truck, so intermittent stuff like this came and went.

Will it engage normally? How does it behave if you just leave it in for a while driving?

My guess is theres a rub in that rear chassis harness somewhere thats shorting out. If it were me I would try running new wires to the locker from the start of that harness under the back of the cab and see if that fixes it. Those harnesses are pretty expensive and I think a 5 or 6 hour job if I remember correctly. Hopefully you get lucky and save a bunch of money by bypassing a hundred different places it could be chaffed.