My Sapphire has the original stereo and speakers. I want to upgrade to a new head-unit and speakers but I am hoping to leave in place and re-use the original wiring to the speakers. I am looking at Blaupunkt or Kenwood head-units with black face plates that hopefully won't look out of place.

First question: will the original wiring connections / plugs fit with a new head-unit. If not are there adaptors available or do I have to cut off the original plugs and use new ones?

Second question: what happens to the fader and bias controls for the original unit? Do you leave them in place or simply remove them from the circuit?