My dads radio finally quit in his 75 so he got the old one out and cut the wires. Now he has no idea what wire goes where on the new radio. There is only one group of wires and the order they go in is blue yellow green green yellow blue. I'd appreciate it if anybody could help me fix my dads mess.

 

The wire colors indicate they went to the old final audio output for the original stereo (see pic). All C3s radioes through 76 were two part units. If your Dad is intending to install an aftermarket stereo, he probably will not need the older wiring. If he is using a stock radio, he will need them.



The assembly instruction manual (AIM) shows how the original factory unit was installed, where the convector mounted, and where things plugged up.

 

He is going to be installing a custom autosound aftermarket radio. What will needed to be done in order for it to work. It needs to be hooked up to the ignition, power antenna, a 12 volt constant, auto antenna and the speakers.

 

solder the connector he cut off back on and get an adapter that will plug into the stock connector.

 

Those wires didn't have a plug they were wired directly into the radio.

 

No, they all have plugs. Those plugs are either still in the rear panel of the radio head, residing with the convector unit (final amplifier stage that is on the finned aluminum heat sink behind the passenger's dash pad), or are still in the speaker wiring up under the dash. There are no provisions for "hard-wiring" things to any of these components, so there are plugs in there somewhere.

If you install a modern headunit, you will need to replace the speakers, as well. The original speakers have (-) terminals that are tied to the [common] speaker housings, and thus to electrical ground of the car. Modern stereo systems use speakers that are "isolated" electrically from the car's grounding system. The speaker wiring connects to the (+) & (-) speaker terminals, but neither of those is connected electrically to the speaker frame on modern audio systems. So, if you try to connect a headunit with "isolated" speaker outputs to the original '75 Corvette speakers, it may not even work. But, if it works at all, it will sound like cr@p due to the poor quality of the C3 speakers and the fact that they are old technology and 40 years old.

P.S. Whether the original unit is working or not, cutting the wires to remove it probably lost your Dad a couple of C-notes in value. The complete radio, convector, and wiring harnesses are still valueable commodities....but not as valuable with the wiring all cut up.

 

He could send it in and have it refurbished and it will be like new again. Reinstall it like it was before.

 

There is nothing wrong with installing a modern headunit/speakers if so desired. But, it needs to be done according to the installation instructions for the headunit. And that will define the kind of speakers and wiring required.