Thanks so much for not only taking him in but making an effort to do well by him and convince him that not all humans are angry creatures who scare him!
My Percy is a blue front amazon and he was not abused perse but he came to me at the age of 5yo and I was told he "hated women". It turned out that that was true but I found out that his previous owner's wife did not like him "at all" and I can just imagine how her dislike of him and the fact that he hated women are linked
Anyway, I am telling you this because you may also run into gender issues with yours because it sounds like his abusers were male. We have been able to overcome (for the most part) Percy's agression towards me and my mother but he still cannot abide unknown women. It has taken me 5 months of constant interaction, trial and error, harassing the kind forum members here for tips

and I've gotten bit many times....but I've won his trust, if not his full respect and love yet. Be patient with your guy, he WILL respond to love and kindness...and treats! My baby looooves pecan nuts and will do anything for them. I use a 1/4 pecan each time I need to coax him into his cage - works each and every time! Find out what your bird's favourite treat is and use that as a reward for the right behaviour. Amazons are very food driven - use that to your advantage.
But please only give him appropriate treats! Like mentioned above, processed meats and the like are dangerous to your bird. Offer lots of fresh foods - he may resist at first if he's a seed junky, but persist. Also, sharing your food with him is a nice way of introducing him to new food. Have a nice raw veg salad and share with him. (Even if you don't like the veg, pretend you're loving it

)
Regarding bathing - I also recommend misting with a fine spray bottle. If he can't or wornt leave the cage, why not mist him in his cage? You can always replace his wet cage liner after you're done and wipe down thew cage to dry it. Introduce the mister carefully though - he may have previously been sprayed with water as punishment and may be afraid of it. Just judge the situation as you go along and stop as soon as he looks uncomfortable. Most birds loooove bathing though, so it may not be too difficult. You don't have to dry your bird and in fact, drying him with certain hairdriers could be very dangerous so rather steer clear. Birds are very good at drying themselves by "shivering". It may look scary (I thought I gave mine pnuemonia the first time I saw it LOL) but as long as he's not in any drafts, he will be fine.
Does he have enough to do in his cage? Toys to play with, things to climb on, etc? A busy bird is less grumpy
Last tip from me - make sure he gets plenty of sleep. I recommend 12 hours to begin - it greatly improves my bird's mood if he's well rested.
Good luck and please let us know how he's doing.