Hi, Bought a 1973 silver face twin reverb of kijiji (Canada’s Craig’s list). Got it for a great price, mainly due to its condition. Good thing I’m into this kinda thing. So I’m replacing a three prong power cord someone added awhile ago from the looks of it. The job they did was not good. Neutral and hot wires wired backward on the aux ac outlet. And for some reason they left the ground switch/death cap wired up. So no problem, all that was corrected, however there’s an added component wired in between the fuse and the on/off switch. Easy enough to take out and return to original, but just in case it’s an added safety feature thought I would ask what it might be. Looks like a diode type thing.