Nice one... I wish I had thought to look at it before upgrading my Sony head unit this weekend. As I pulled it out the four speaker wires came off their plug, I could see what order they were lying in left to right but had a 50/50 chance of getting the plug up the right way! I guessed and it sounds ok; but now I know it is:
Left Front - White
Right Front - Black
Left Rear - Yellow
Right Rear - Red
I will have to pull it all out again to check as I will never be satisfied otherwise!
And yes - no excuses for not upgrading those eighteen year old speakers now either

Cheers all, Rob