Another Stereo question?????

Another small problem on my P38! It's got the HK system (certainly the subs are in the boot and the CD cable is there but at some point some muppet has changed the head unit and removed the cd changer! Anyway, behind the dash somebody has spliced and heat shrinked 2 fairly thick cables (with approx 5 individual wire each) together. Any ideas??? And also they've hacked about with some of the wiring, especialy the red plug (appears they've cut off a piece of the plug to make it fit a new head unit). My main other questions are can anybody tell me what connectors should fit the back of the standard stereo (as apart from the grey and red block connector/ariel I cannot see the steering wheel control cable or the Cd changer cable where it should plug into the head unit), and also what model of stereo should be fitted as I'd like to put it back to standard to get my wheel controls back/decent sound etc. My P38 is a Sep 98 4.6 HSE if it helps. Hope it all makes sense ands once again thank you for all your help in advance!!