The parking brake will requires regulated pressure and 12V electricty to get it off. It is spring applied and hyd. released. The other key is that header will not move. This circuit also requires 305 psi regulated pressure to make the high pressure oil go. Suspect the regulated spool in the regulated valve is sticking or the reel drive valve is not providing sufficient back pressure to make the regulated valve work. e-mail if you have IJ's.