Hope you find link ok. I carried out this exact mod for a head unit I bought last week to replace a cd skipping Bose unit. It's only a matter of cutting off the RCA plugs (red,yellow,white and black). When you then strip back each cable you will first find stranded wire around an inner bit of PVC cable. This stranded wire when wound together is the -ve. When you then strip back the inner wire this is the +ve. These 2 wires are then connected to the speaker output from your new head unit. The colour of the inner insulation is the colour you match it up with on your stereo ie if green inner insulation, inner core goes to green speaker wire and outer stranded wire goes to green/black. Repeat this for other 3 RCA plugs. I used heat shrink to stop +ve and -ve wires touching after soldering. Hope this helps.
Regards Richard.