Along with the fender PA amp, my mate asked me to have a look at his Crate Vintage Club 50 guitar amp, more specifically, the short FX Loop breakout cable I had made for him, the complaint was that it was getting a return signal, but wasn't putting-out a send signal, after doing a couple of tests on it I managed to figure out what was going on, turns out it was simply due to me incorrectly labeling the two 1/4 inch sockets on the little diecast box on one end of the FX Loop breakout cable, I had the send socket mis-labeled as the return, and vice-versa.....how embarrassing for me, eh?, oh well no real harm done and at least that proves that I'm a human-being that makes mistakes after all, anyway it's all good now.
Moral of the story....always make sure that you quadruple-check to make sure you've got it right first.