Faulty fuel gauges

[dach side]

The setup: two sets of fuel gauges, port gauge on bridge & stbd. Gauge at lower station don't register, but others do. I'm guessing this means the senders are working, but where should I start looking fou the inop gauges?

 

[High Wire]

Assuming they were working recently and now are not. Trade a working gauge for a non working gauge. If the problem changes location, its the gauge. If not, its the wiring.