It might be easier if you actually tell us the brand name and model number of the unit. If you can't figure it out for some reason, post pics of the case and the face of the unit. If you have a yellow with blue wire and a yellow with black wire then it is an Alpine. You will need a PAC TR7 bypass for it.

We can't help you at all until we know what head it is. These days, almost no headunits are bypassed by simply only grounding the park brake wire. Manufacturers are a little smarter than that. But, they are ALL bypassable...