I had the same exact problem:
I finally fixed it (I hope) this past weekend after several months. I can't say conclusively that it was the rectifier because I believe I had other problems going on too. SInce the coupler was melted, I just assumed it was a bad rectifier. I would think it had shorted from my wires touching.
Also as the prev post said, is your battery new? I neglected to look into that and that was one of my main problems of my bike not holding a charge. My battery was old as dirt. I swapped in a new coupler, rectifier, battery and also another cause for suspect for electrical probs on my bike (fuel pump relay) and everything is working great now. I took someone's advice of checking for a drain by setting up a bulb in series when the bike's off to see if there is something draining it and I didn't detect anything after I swapped all the new stuff in.
battery drain checking advice
Good luck. Electrical probs are a bitch...