Oh how many standoffs DS and I have had over the years over basic self care functions before the dots joined up and his SNs became clear enough to be referred and diagnosed, including sensory processing disorder.
He's the kind of child who arrived half way through his brother's birthday party after an hour long stand off/ meltdown over brushing his teeth. He was 8 and he wanted to do that activity too! (It turned out that he was stewing with jealousy because his brother would get presents, sometimes the dispùte is a proxy issue of control over another problem)
Hair brushing is also one of our difficulties, and he has shoulder length hair so it is important to manage it.
Have the right tools. Hair oil helps smooth it and reduce pulling. Washing helps if it is really matted (especially as he's having a hair chewing phase) Have a suitable comb/ brush for the hair type.
Have well maintained cuts. Straggly, split ends are harder. DS is no fan of hair cuts either, but has conceded that yes it is now easier to comb without an inch of mangled ends.
Back off if it you are not time critical. Don't give up, but say that it will happen, but you can have some time to calm down.
Incentives. When we have done this, then we can do that.
Making up is important. Own your own actions. Explain why the hair brushing is important but don't get blamey. Make-up hugs work well in our house. Yes we have our run-ins and sometimes they overwhelm our patience levels, but we always love each other and feel secure in that love even if behaviour is sometimes difficult to manage.