4x4 ford excursion
 

i need help guys i have 2001 ford excursion 7.3 i had ford run a test on the system and they are saying the PVH Solenoid may be bad well my guy here at the shop took it off and tested it and it was fine with no open trace like they said. when i turn the high/low switch no light nothing not sure what to do.
any advice please help