Cables built to the standard are the same for both modes. Most modern switches do not support Mode B. I've never heard of a switch supporting Mode B, although at least one must certainly exist.
OK, so you're using an injector, where 7/8 DO matter. One remote possibility is a mistake I made on one cable, where totally not visible looking at it, the stripper cut through one of the wires leaving the unconnected end firmly attached by the uncut part of the insulation. But since you had the same failure multiple times, this is a low probability explanation. Maybe this was already covered, have you run a known-good cable on the tester, to test the tester?
OP didn't state what type of POE switch he had and if he was trying to power the POE device using mode A or mode B. Most modern switches can automatically determine which mode it is. He said he wasn't getting any power on pins 7 & 8, which in mode A, isn't used. Assumption was made that he was attempting to power it in mode B as the wiring sequence for his RJ-45 connector would dictate. I am going to bow out on this discussion. You gents have your self a good evening.
