If you can clean it, do so with a good dollup of liquid soap, rub around a bit, and hose off. Alternative to soap/water would be a generous amount of peroxide on the entire sore area...perhaps a couple times. It sounds like its been infected with fly eggs/bots or something else disgusting that will grow and fester so its something that really needs to be cleaned before any medication could be applied...after cleaning, any antibiotic ointment would be helpful, like Neosporin or Betadine ointment or similar.

sounds like Fly Strike. Google it to read more about it. This seems to be happening a lot. Neosporin is probably good advice until the vet can look at it. I don't know about the mites. I suppose that could be it too.

Do you live near the shore? I grew up in NJ and spent every summer getting eaten by the greenhead flies @ Island Beach State park.

They are awful!

especially the ears as the flys that are blood suckers do love the ears because the blood veins are close to the skin there. Here in NJ we have those green flys that suck the blood so that is what I do when my dogs are in the kennels. It also helps to have something around that draws and kills flys I use golden Marin, get it at Agway. They also sell bags (clear plastic ) with a stinky capsule in them that you break and fill the bag 1/2 with water, then hang it somewhere where most of the flys are. The flys can go in but cannot come out.
How you describe the ears is exactly how they look from flys biting them , it is the flys that cause the problem and not a problem with the ears that attracts the flys.

any kind of open wound, could be some kind of fly, scabbing, infection, dried blood. Yuck, poor guy. I hope he gets attention soon.

nm