If you do not own a multimeter here is a link to an inexpesive one from Home Depot - http://www.homedepot.com/p/Powerbuilt-Digital-Multi-Meter-648349/204505225
If your cab bus and / or cabs are not working correctly or your cabs have display issues you might have a low voltage dues to loss from cable length. The minimum operating voltage for the Cab Bus is 8v DC as measured on the UTP Panel.
Use this link below to calculate your cable loss. NCE Cab bus cables use 26awg wire in our example below 40 feet of cable results in 27% loss reducing the cab bus voltage from 12VDC to 8.7VDC which is very close to the minimum operating voltage of the cab bus.
The overall goal is this: A minimum of 8v DC as measured on the UTP Panel and cab bus cables between pins 2 and 5 / Black and Yellow.
***Note, you must DOUBLE the length of your cable!!!
** Results may change with real wires: different resistivity of material and number of strands in wire