I work on heavy tractor trailers a lot, and I have a few circuits that I have to diagnose frequently that the circuit is open. The wire which is a twisted pair breaks at some point in a 15 foot section of harness. It is a loomed harness with about 20 wires inside. I am going to purchase a signal generator/open finder if they actually work. Any experience with any of the different models out there? Thanks for any help.