I recently installed an aftermarket unit and utilized the provided diagrams plus the ones online, but even after all that, when I have the designated red(accessory/switch) and yellow (12v constant) together it lowers up and works, but have to turn it off manually, any help would be appreciated:

 

You need to hook the red acessory wire to a keyed on off, that is why you have to manually turn the HU off. You never hook the accessory & constant
12V together.

Did you buy a harness adapter? If not you need to. It makes instalation mucch easier.

 

I bought the adapter and tried wiring the keyed accessory and constant separately, but I would have no power to the unit