Hello, System is over 25 years old. Hasn't run in over 10 years. Park, 8-10 acres. Repairing busted water lines everywhere. Found 2 valves with the 521a. Using the 521a to locate all my wires. 8 strand multi colored. Working on identifying nicks and breaks. Found a 20' gap under a mature Pine Tree. Unable to continue trace past this point. Repairs made to busted pipe located beyond this spot, spliced into this multistrand at this point to pick up the trace. 8 strands 4 colors...2 black....2 green....2 yellow....2 red....wtf? Not to be intimidated, I continued with my trace until I ran out of range of the transmitter. My question, how can I determine which one is the common wire? I need to find the valves. [short of running my aerator down the wire line which I am temped to do at this point] Thank you in advance for your help, kenny.