What is the best way to wire THREE speakers to FOUR outputs?

[larrylamb11]

When fitting a head unit into an old car with a single, central dash-mounted speaker together with a pair of rear quarter panel speakers, what is the best way to wire them all to achieve the best balance and sound?
Obviously the rear quarter panel speakers can be wired into the Rear Right and Rear Left outputs from the head unit; but what output should the central front speaker be wired to?
Is there a standard protocol? would I be best to wire it using Left -ve and Right +ve? or wire both -ves and +ves to the one speaker?....or just wire it to the first output that comes to hand?

[blueacid]

Don't go trying to combine two different amplifier outputs unless the amplifer is configured to expect this (bridged mode for instance).

I'd suggest just wire up the front left or front right; for the vast majority of material you really won't notice; it's only if something is played exclusively out of the opposite speaker to the one you connected that you'll notice. Stuff like The Beatles where the singing is predominantly in the right channel and the beat is in the left channel.

[Dr Doofenshmirtz]

If the head unit has a MOSFET amp (it most likely has) then you can bridge the outputs no problem. Connect one of the speaker wires to the + (positive) and the other speaker wire to the - (negative) of the other amp. You now have a mono centre speaker with twice the output level of the other non-bridged speakers.