A highly practical network installation and troubleshooting tool which features a single or multi-tone signal, two test leads and a 4-conductor modular cable. The tone generator's signal is easily traced by the probe, even when cables are in a bundle or hidden in a mess of punch down blocks or wall plates. This system verifies cable continuity, identifies wiring faults, and determines line polarity and voltage in network and modular telephone lines without damaging cable insulation.