There were three radio options (plus a radio delete) for the Eldorado in '74: AM/FM radio, AM/FM stereo with auto signal seeking radio and finally, AM/FM stereo with (8-track) tape player. My car came with the AM/FM stereo with auto signal seeking radio. The radio itself is rather cool, it was the pinnacle of analog mechanical radio tech. When you push the signal seek button, a motorized tuner turns the tuning dial up and down the band until it hits a station that it can tune in. Also, when you switch from AM to FM, the indicator display flips over to show the proper frequencies for that band.
BUT... This is a car from the '70s. It MUST have an 8-Track player in it. Long ago, I had a '74 Coupe deVille and in that Coupe deVille, there was an 8-Track player. I took that 8-Track player out, stuck it in a box and put that box in the attic of my parents house where it sat until just recently.
While I'm sure the this old 8-Track player "ran when parked", it certainly did not work now. It's common for the mode switch to get corroded and make the entire unit not work. It's the white plunger just under the belts in the middle of the pic below.
On top of that, the belts for the 8-Track were shot, the capstan had old tape wrapped around it, the head position actuator was stuck, the volume pots were scratchy, and the radio preset buttons were frozen. Repairing this was just a "one thing at a time" kind of thing. First up were the belts. Just order new belts and that was it. They are cheap and easy to fine.
Next up was the capstan. It's the post in the middle of the big flywheel and it's supposed to be clean and slightly rough. It presses against the rubber wheel in the 8-Track tape and it's what pulls the tape over the tape head during playback. It was neither clean or slightly rough anymore. I pulled off the old tape, masked it off, and sandblasted the area where it should be gripping the tape.
Next up was the head position actuator. For those who don't know much about 8-Track tapes, the tape has 8 individual tracks (duh) on a 1/4" wide tape. They are divided into pairs for left and right stereo so you have four pairs of track on a tape. The tape itself is about 12 minutes long and you have 4 of these 12 minute long tracks per tape. To switch tracks, you push a button and the tape head moves down two tracks to the next pair. Keep pushing the button and it will cycle all the way to the bottom and then back up to the first pair. The tape will also automatically switch tracks at the end of the 12 minute recording. This is possible because 8-Tracks are a continuous loop. When you play the tape, the tape is pulled from the center of the spool, over the tape head, and then wound back on the outside of the spool. The splice between the beginning and the end of the tape loop has a conductive tab and that tab bridges a circuit during playback which switches the track selector. As a side note: it's impossible to rewind an 8-Track tape. Some machines could fast forward but it was really hard on the tapes themselves. Here is the actuator. It's a cam system and the problem was the old grease had hardened and was gumming up everything.
Now for the volume pots. I just used Deoxit spray on the pots and that cleaned them up.
I cleaned the mode selector switch the same way.
