dual speakers with only 3 wires

Hello,

I have some Recaro seats with dual Blaupunkt speakers in the headrests. I am trying to hook them up to my deck, but there is only 3 wires and not 4 from the speakers. Using a 9 volt battery I have found that they seem to be sharing a ground wire. Can I hook the positives from the speakers to the correct positive of the deck and the 1 ground from the speakers to a single ground off of the deck, or should I combine both grounds from the deck and connect that to the single ground from the speakers? Any help would be appreciated. I would have just connected my own wires right from the speakers if they weren't sewn into the seats. Thanks

A ground is a ground, if it is a ground.   If your radio was manufactured in the last 15 years or so, chances are it is a high powered unit.  This means that there is signal on the negative speaker wire. 

I would not try connecting the negative speaker wires together.

Sorry,

I think I labelled the wires incorrectly. There is a common wire between the 2 speakers is really what the post should have said. I don't actually know if it is a negative or positive. Just that it works with both speakers. With this being the case, I am looking for help in how I should wire up these speakers. Sorry if I didn't explain this well in my original question. Thanks

I'm wanting to say that the speakers are sharing the ground, they are probably 2 8ohm speakers in parallel for a 4ohm load on the amp (if they are 2 4ohm speakers in parallel for a 2ohm load, your HU's internal amp may not work). I think you should connect both +'s from the left headrest to either the left front or left rear +, and the the one - to the same output channels' -. For the right headrest, do the same, but on the right side of the HU's outputs (the same, front or rear, as the left side).

You really need to do some impedance and polarity checks first.

The speakers are mounted in a seat.  there is one on the left side of his head and one on the right.  

It would probably not be too hard to remove the top half of the seat.  Then you should be able to get the fasteners on the bottom of the seat back.  Remove the fasteners and you should be able to slide the cover off of the seat and rewire the speakers.

It could be an old seat.  But your point is well taken: the speakers could safely be used mono on one channel of an amp that can handle the impedance.

I ditto that point. However, having one half of a stereo signal right behind your ears would really suck sonically. I could see using two channels bridged so that you at least get both channels merged instead of only one half of a stereo signal. If you were to play any music with that is recorded with any degree of separation, the sound would get hollow depending on which side had the vocals, etc.