Using a stereo head unit with mono speakers

My car (1976 Ford Gran Torino) is set up with a single speaker in the dash and two 6x9's on the package shelf. There is a fader knob under the dash which moves sound between the front and rear speakers. There is a Philco AM radio in the dash which works, but I want FM sound without adding a converter. This AM mono radio has four wires to connect in the back. One for power, one for the dash lighting, one for speaker positive, one for speaker negative. Ground is through the radio's chassis to the dash frame.

I have been searching unsuccessfully for a year to find an AM-FM mono radio from a 70s Ford product. They either sell for over $50, or are stereo radios with the "STEREO" lettering rubbed off and they have 7 total wires. One for power, one for dash lighting, one positive for each speaker (x4) and one negative common speaker ground which branches to each speaker in the harness.

I am about to give up on sourcing the mono radio. I would like to purchase one of the stereo radios (or pull my own from a junkyard as there are four with the old style all-weather plugs like I need in good condition in the self-service yard near me) and go with that. The problem being I want to hear both channels but I don't want to replace any factory wiring. Any modifications need to be made at the plug.

How do I take both LF and LR signals and the common ground (3 wires in total) and connect them to two wires? Can the LF and LR signals both travel along the single mono speaker wire? Will the common ground wire hold up with two speakers' worth of sound going through? Or should I bypass the fader unit, run left channel to the front speaker and right channel to the rears? What would be less hassle?

 

It's also not just a matter of spending the $50, it's finding one on eBay when I actually have the $50 to spend. They seem to pop up when I am spending money on things like brakes, or chasing down electrical problems, or putting a water pump on the wife's truck. There is also the matter of finding the radio in 74-79 style with the same lettering as my AM radio, as the 71-73 mono radios have a different face and although they'll fit, they'll look different from the rest of the dash controls.

I'm picky.

But I think I found a solution.

http://www.crutchfield.com/ISEO-rgb...nd-R-57N.html?o=ptp=5684&showAll=N&tab=review

This is a 5x7 stereo speaker that would replace the dash speaker. I can wire it up seperate from the factory harness using LF and RF speakers from a stereo radio tuner. Then I can bypass the fader on the dash (since the radio will have its own fader on the outer ring of the tuning knob) and run thick LR and RR wires under the carpet to the rear speakers. The power/backlighting plug is the same for either mono or stereo. And if I want to add an amp inline to the rear speakers I can do that. And obviously replace the stock 6x9's with something better. A 200-watt amp and 200-watt speakers should do the trick nicely and except for the amp bolted under the package shelf, nothing would be visible.

Do low-power amps like a 200-watt unit get hot enough to worry about heat soak? Can I build a small enclosure around it to hide it completely, or will it get too hot that way? I also thought about mounting it above a wheel well where it'll be up in the quarter panel and not visible when the trunk is opened unless you shove your head down over there.

 

Sorry, what I meant was use that 2-in-1 speaker in the dash, wire it up to the LF and RF speaker wires and grounds. Then either re-use the stock wires for the rear speakers (if it actually runs seperate wires and doesn't just split off in the back) or run new wires. And if I do go with a small amp out back I'll want new wiring anyway to handle the power cleanly.

My seats and carpet are coming out anyway at some point. I can live without the rear speakers until that day. I have to restore some of my weatherstripping first so I don't put good new carpet into a car that gets wet inside when it rains. The seats not so much, I'll be using solid vinyl. But I'd like to do all this at one time, seats, carpet, speaker wires, weatherstripping, rear window seal, package shelf, et cetera.

But if RangerSVO's contact has the radio I need, I'll live without stereo sound (happily, mind you) and go with that! The fewer changes I make to this car, the better, because I like it the way it is. I just want FM so I can broadcast my iPod through it. It's either that or build an AM transmitter. I actually went in my local Radio Shack and priced out the kit and bits I'd need for one. I then wandered over and looked at all the FM transmitters and iPod adapters and asked about what to use for an AM radio and the kid said, "why not just switch the button over to FM?" I snickered a bit and walked out.