ISX Cm871 cutting out

[08kent800]

I have a 2008 kenworth T800 that I recently bought and it has the ISX Cummins in it. I’m having trouble with it cutting off when under acceleration. When it’s cold and you first start it up and start driving the rpm will not read over 1000rpm after it cuts off once while driving the rpm will read correctly and sometimes once it cuts off the next time it won’t read at all. I’ve tried the tap test on the ecm and it won’t cut off from being tapped on. And I found that one of the main 2 main power wires in the 4 pin connector doesn’t have power the grounds are good and the other wire has good power. I traced the wire back to a fuse just below the ecm and the fuse is good and the circuit reads good to there but I can’t find where the wire goes to from there.
I appreciate Andy help on the subject!