I am getting a remedial course in network wiring this week. I’ve been lucky in the past, as all of my CAT 5/6 wiring has “just worked”. Sadly, my luck ran out the other day, when I tried to rewire the uplink for a 5-port switch in my basement office. I have two uplink wires running to my basement patch panel, and oddly, the switch’s jack worked when patched through to one of them, but not the other. Both uplinks worked when I plugged my laptop into them directly, so I was rather baffled. At that point, I decided it was finally time to invest in a network cable tester. I picked up a Klein LAN Scout Jr 2 from Lowe’s, and it immediately identified the problem: The switch’s jack’s wiring was bad (pins 1&2 open), uplink 1 was wired straight, and uplink 2 was wired crossover. The good news was that of the 7 jacks I tested, only 2 turned up bad, and they’re both short runs that wouldn’t be too hard to replace if I choose. Interestingly, both of the older jacks that I rerouted to the patch panel were wired crossover. It was 10 or 15 years ago that I installed the jacks, and I thought I remembered wiring everything with T568B, but apparently, I was wrong. I probably won’t bother re-punching them, as I don’t use either jack much (one of them I had actually never wired up) and they both still work thanks to Auto-MDIX. I do know now to check the wiring at the other end before punching a wire in to the patch panel (you’d think that would be obvious, but this is me we are talking about). As for the bad jacks, I’m not sure if the issue is with the cables or the punches (or both), but either way, it’s good to have a way to test the wiring. As a case in point, I crimped an RJ45 plug this evening, and accidentally swapped pins 1 and 2. Without the cable tester, I likely wouldn’t have known about it until something didn’t work right, and then I would have been pulling my hair out. I’d say the tester paid for itself right there.