Car Stereos: 1967 Lincoln car radio, radio chassis, ac volts

Question
I am restoring the Lincoln. 2 of the 4 speakers are missing, remaining 2 are slightly torn. New auto store speakers will fit but are listed as 4 ohm. I think '67 radios used 8ohm. Will 4 ohm work? Also my car had a optional but non working AM with 8 track player. I bought a ?? working original AM/FM what I wish to install. I expected that all the wires would change over but the speaker wires are different. Can I turn the radio on and touch speakers wires till I get some to work? Thanks

Answer
Hi Bill,

I'd be surprised if 4-ohm speakers didn't work.  I'm not an expert on older car audio systems like yours, but 4 ohms has been standard in car audio for quite some time.  

I have to admit that I don't have a lot of information on the older Lincoln AM/FM radios.  It's very likely that your radio uses a common-ground speaker setup; for example, a common-ground 4-speaker output would have four positive speaker wires and a single, combined negative wire (or it might connect each speaker's negative terminal directly to the chassis metal, and use the chassis as the speaker ground).  If you're able to get the unit to power up, then you can use a multimeter to identify the speaker wires.  Just set the meter for AC volts, and test each wire for AC voltage with the radio playing.  The voltage measurement will vary with the audio, but it will generally increase as you turn up the volume.  (This is one case where an analog meter, or a meter with a bar graph, works better than a meter that just shows you numbers).

You can try just touching the wires to the speaker to identify the wires, but the speaker would need to have a positive and negative connection--for example, if you connect two positive speaker wires to the two speaker terminals, it won't play.  For a radio like yours, it might work if you wire one speaker terminal to the radio chassis (or vehicle chassis metal) then test the speaker wires on the other terminal.  This is something that wouldn't work on a modern head unit, but it should work with yours.  However, do this only if you're sure you've identified all the power wires and the power antenna wire--if you mistake the power antenna output for a speaker wire, and connect it to a grounded speaker, it might damage the output.  If the radio is equipped with a power antenna wire, you can identify it with a multimeter--it should show 12 volts DC whenever the radio is switched on, and no voltage when the radio is switched off.

I apologize for the late response to your question.  I'm still catching up after a windstorm that knocked out power in my area early this week, so my internet access has been limited.

Hope this helps!

Brian