If you see blackened lamp sockets, hear arcing electricity or smell the odor of burned wiring when you open the sign, don't bother testing. Remove all the lamps and open the raceway covers to inspect the sockets and secondary wiring. This is particularly true when the socket raceway is located on the bottom of the sign where water collects. However, sight, smell and hearing aren't always enough to find a problem. To test any ballast, begin by checking the primary input voltage with the lamps and ballasts connected to the circuit.
Low voltage caused by overloads or undersized feed wires is the most common problem.
But the voltage drop won't show up on your voltmeter unless the sign is connected when you test. If you notice that the insulated, primary wires are very warm or hot to the touch, the wiring is probably too small for the connected load. If any significant voltage is present, the cabinet is not properly gounded. In this case, it should not be used as a substitute for the neutral wire when testing. Because ungrounded signs are hazardous and troublesome, this problem should be corrected as part of the repair.