I know I have made some errors with being a good pack leader
First error: Buying into the whole idea of "dominance", "alphas", and being the "leader of the pack". Look up Cesar Millan, his training philosophy is as incorrect and wrong as it gets. The "alpha/dominance" theory has been disproven and rejected by trainers and scientists alike, including the ones who developed the idea in the first place. Dogs don't feel "dominant". They just don't. People like Cesar Millan try to use "dominance" as an explanation and/or solution for just about everything, when in reality, it's not a factor at all.
Dogs naturally look to humans for guidance, so if you are a consistent and firm- yet gentle- leader with boundaries, rules, and rewards, and a good bond with your dog, there's no need to prove yourself as pack leader. That can actually lead to behavior problems, anxiety, or aggression, and could even contribute to the kind of behavior your dog is exhibiting.
I'm not saying you can never (respectfully) correct your dog, or that you should just let him do what he wants, rewarding for good things and hoping he does nothing bad. Just know that the goal in training is teaching an animal (who already has some desire to please you) what you want and how to do it.
Now for the answer to your question:
When your dog gives a warning, like an angry glare, or biting the leash, listen to him. He is telling you he's uncomfortable. As his protector and trusted ally, it is your job to help him become more comfortable, not to continue, hoping he will get over it.
---Step one is to identify the issue- why is the dog uncomfortable? Perhaps there was some unpleasant event he experienced associated with the harness, even something as simple as his hair being caught in the clasp and pulling. Perhaps he finds the leash too heavy. Perhaps there is something itchy or otherwise uncomfortable about the harness. (Is it too tight? Is it a no-pull that uncomfortably tightens? Is it rubbing/ chafing under his legs?) Or perhaps he simply wasn't properly introduced to the harness as a puppy and is finally fed up. (did you just put a harness on and leave for a walk, or did you take it slow, letting him sniff it, be comfortable with it touching him, with it draped over him, with it partway on, etc.) It's not too late to go back and re-condition him to a harness now, that may be helpful no matter what the problem is.
----Step two is to listen to his warnings. If you get out the harness and he seems nervous (licking lips, ears back tail tucked down, showing whites of eyes, etc.), don't go any further. Put the harness on the floor, and make it a positive experience using treats or play. Get as close as you can without him getting nervous, and slowly work up from there, never pushing your dog past his comfort zone, until you can put the harness on no problem.
---Step Three is similar to step one . Identify anything you are doing that could make him more scared. Are you wearing a hat, coat, (especially a big one) or gloves that he isn't used to? Do you crouch next to him, or do you loom over him, bending over to put it on. (can be scary, especially for a small dog)
It's good you realize yelling wasn't a good idea. It's certainly not an unfixable mistake, though, dogs do forgive. For that one negative association, make sure he has hundreds more positive associations with the harness. And just remember in the future that it's ok if your dog shows his teeth, growls, even snaps or barks(and if you ignore those warnings, bites). This is the only way he has to communicate with you- he's not being aggressive, (or dominant) he's just telling you he's unhappy. Listen to his warnings, and NEVER punish these warning behaviors, as it teaches the dog to stop warning and go straight to biting when scared. When he communicates, listen, and fix the problem. (he growls when you clip the lead on, so unclip it)
Make sure you don't surprise him with the harness or lead, he could have just been startled that first time.