splicing existing speaker wire

My fiend and I are installing two 12 inch subs in the back of his '87 grand am. We were wondering if we could splice the rear speaker wires in order to save the speakers or should we just run separate wires from the head unit to the amp. I figured we should just cut the rear speakers and run them through the amp. But we don't want to loose the rear speakers. What should we do?

it's factory

You don't need to cut the wires.  For simplicity, if the amp has high level inputs, run jumpers from the rear speaker wires to the amp inputs.  If not, use some line out converters off the rear speakers.

See the post about lineout convertor necessary.Top Secret, I can tell you but then my wife will kill me.