I am involved in a wire harness manufacturing business that builds very large wire harnesses with many circuits that are usually branching out over a large area like a 4ft. by 8ft. or even larger build board. Usually we just buy a circuit tester which is very expensive and overkill for what we need which is just to see that a wire circuit is properly housed in a connector and placed and run through the harness to it's other end where it should go. We only need to verify the circuit. The bought harness testers are slick but at 10 k it becomes a financial burden especially when we need many of them for all sorts of harnesses as we expand the business. So I thought it would be worth the look to see if there is advantage to building a DIY system . The bought system can learn a known good harness and store it in memory (called up when you need it again) once it is put on the harness test/build board. Presently I build an interface from the board to the tester which involves running wires from mating connectors to the tester and placing the mating connectors on the front side of the board so the build person can plug in the various parts of the harness and build a complete harness. The bought system also monitors the build in real time so that if a mistake is made it beeps to alert the build person. The bought tester has a standard 256 connections and then you have to buy add on sections each time for another 256 at 1500 for each 256 test points. I need at least 512 and sometimes more. So what I'm looking for suggestions from some knowledgeable folk on which way to approach design of this tester. I'd like to use an arduino if possible to housekeep counting and logic. Not sure but some sort of multiplexing system or if there is some sort of cascadeable addressable logic switch out there that I don't know about or some other LSI that would help. I've attached a simple drawing(paint) to explain the basic idea.