Car Stereos: cd changer to vintage analog car radio, fm modulators, unit conversions

Question
Hi; I recently had my stock 1962 Mercury radio converted to FM stereo with 4 RCA speaker output jacks and what was described as an 1/8" female stereo jack to allow an accessory such as a CD  changer to be played through the radio. It has no added aux knobs. I have tried several "universal" CD changers with FM modulators, but they require the radio to be tuned to a certain FM frequency. I can't get any sound from the CD even when I find the FM station on my radio. I have NO DIGITAL frequency reading on the analog dial face of my radio. Is that the reason the CD changer won't play? Also is there any alternative connections, adapters, switchers or CD changers I can use to either play through my radio OR the speakers. Thanks

Answer
Hi Paul,

I apologize for the extra-long time it's taken me to answer your question.

It shouldn't be necessary to have a digital FM tuner to use an FM-modulated CD changer; as far as the head unit is concerned, a CD changer modulated to 88.3 FM (for example) should be indistinguishable from an actual radio station broadcasting on 88.3.  With an analog tuner, it might be a bit tougher to find and lock in the frequency, but once you've found it you should be able to hear it without a problem.  Unfortunately, I don't have any idea why it's not working in your case.

If you want to play a second audio source through your speakers, it will require some sort of amplifier.  If it's not possible to use the head unit's amplifier, then you'd need to install a different one.  There are a few options; you could install a hidden amplifier to run the speakers, while still using the head unit as a source, but with a switch so that you could change the source to a separate CD player or portable audio device.  Or, if you have a hidden spot to install an alternate head unit, there's a method of switching the speakers from the original to the second head unit when you want to play a CD.  

I'm not familiar head unit conversions like the one you've described, but I'd think that if there's a 1/8" stereo auxiliary input, there must be some way to select the input as an audio source.  You might find it easier to use a small portable MP-3 player or iPod to play your music, rather than a multi-CD changer system.  

Sorry I can't be more helpful!

Brian