The tape deck in our stereo broke shortly before a road trip out West. The ejecting drive gear sheared off a few teeth (from age and plastic deterioration most likely) and it took a minor operation to eject any tape. While we don't listen to tapes any more, we do use a tape adapter to listen to my laptop, digital music, or CD's. We also wanted the radio to work, but with a tape stuck in there, it wouldn't play.
I had an old Sony EXR-11 car stereo on hand which a previous roommate had left after upgrading. But this Sony Stereo did not have the same connectors as the factory default from Ford. But this wasn't daunting as I could assume the stock speakers were within the limits of the Sony output. All I needed were wiring schematics to translate the connectors. This proved to be a challenge.
The hunt for schematics was harder than I expected. I eventually found the car stereo wiring schema for the Mercury Tracer (and Ford Escort) at The Install Doctor (a nice site, by the way). But if they are missing, I've saved the schematic and attached it to this page.
The Sony stereo schematic was not so hard to find, but all I have left of that is a JPG I screen captured.
Once I had these schematics, I need to decide how to physically join these two female connectors. I decided against cutting and splicing the wires. These connectors are very useful with you have the right stereo. Instead, I created little, flat inserts to bridge these connectors.
I removed the connector shell on the Sony wires, baring the flat prongs. I inserted my "splicing inserts", made from aluminum can strips, folded and trimmed. Then I just connected the proper wires, wrapped it up in tape, and TaDa! It worked! (If I ignore the hours of trial and error troubleshooting before I perfected the thickness of the inserts, tape wrapping style, and how to re-insert the stereo without breaking any connections.) The new car stereo worked great—better than what it replaced too.
Once I had these schematics, I need to decide how to physically join these two female connectors. I decided against cutting and splicing the wires. These connectors are very useful with you have the right stereo. Instead, I created little, flat inserts to bridge these connectors.
I removed the connector shell on the Sony wires, baring the flat prongs. I inserted my "splicing inserts", made from aluminum can strips, folded and trimmed. Then I just connected the proper wires, wrapped it up in tape, and TaDa! It worked! (If I ignore the hours of trial and error troubleshooting before I perfected the thickness of the inserts, tape wrapping style, and how to re-insert the stereo without breaking any connections.) The new car stereo worked great—better than what it replaced too. 
