Styling mk2 factory fit sub

[gazmaniandevil]

i have a mk 2 punto active, with the factory fit boot sub, when i changed the original head unit (which i swapped for a normal blaupunkt cd player) the leads just plugged in as normal, the one lead tho which i presume powers the sub causes awful feedback, is there a converter lead for it or does anyone know what it does actually do, the other speakers seem to wrk ok with just the first leasd plugged in,