Running lights not getting power

Hi any info would be great - 2005 kw w900l

All lights were working perfectly...stopped in truckstop last night with truck on idle....all the running lights flickered once then went out...including the light bars on the air cleaners which are wired into the same circuit.

Pulled and tested all fuses...not the problem

Used a screwdriver electric current tester and there appears to be no power coming to the fuse pocket for that switch compared to the fuse pocket for the trailer lights for example

I was going to pull and check all the bulbs but before i do any ideas where or what to look for since no power going to the fuse for that particular circuit.....seems to me if it was a bulb problem that would not affect the power to the fuse pocket??

When a wire was dodgy on the air cleaner set of lights previously it just stopped them working not the whole lot.

Thanks in advance