Is he having problems with the halter,the bridle, or both?
I ask because you wrote bridle in the original post, but halter in this latest post, and I'd approach them a little differently.
If its the halter, maybe he had a bad experience with one when he was initially rescued? Or, maybe his ears hurt (ticks, mites, other bug bites). One of mine HATES having anything pulled over his ears. He's otherwise calm and easy-going, but pull somethig (bridle, halter, reins, flymask) over his ears and he flips. His previous owner thinks it stems for sore ears from tick infestations when he was younger.
What kind of halter do you use, rope or buckle? Have you tried using a different type of halter? What about the lead rope? Is he OK when he sees that? Have you ever tried looping a lead rope around his neck and walking him around the pasture a little with that?
If he tolerates the lead rope around his neck OK, then I'd probably try doing that for a few days, and then start slowly introducing the halter to him. First let him see it. Then touch him with it, let him see that it doesn't hurt. Once he's OK with that, I'd try looping it around his neck. Work your way up to getting onto his head. Keep the lead rope around his neck (hold it together under his neck in one hand) until the halter is on, then take hold of the halter and snap the lead rope on.
I have a padded halter that for some reason, my paint decided has the
devil hiding in it. Normally, I can walk right up to him and put the
halter on without any problem. The first time I used the padded halter,
I put the one part around his neck, reached my hand over his neck to
grab it, and went to put it over his nose when -- bam! -- horsey
freak-out. I got him to tolerate the padded halter by restraining him somewhat with the lead rope before putting the halter on, so that even though he tried to get away, I still had contact. But, the restraint is loose enough that you can just release the lead rope if the hores really freaks out.
Make it pleasurable for him, with lots of whatever it is you give him as a reward, be it treats, carrots, a little grain, or a scratch in his favorite place.
Good luck!