6 x 4 electrical problem

Have a 1999 6 by 4 diesel. One day it works and then next day does not. I have tracked all wires to make sure no problems there.

When it does not work the dash lights come on real dim. When its running dash lights bright as always. Local john deer shop cant seem to find the problem because it never stays broken long enough.. Till i get it home and down it goes again.

Any suggestions all help wanted