The radio on my 96 Ranger quit working so I bought a aftermarket radio and a Metra harness adapter, I got everything hooked up and now have some whining coming through the speakers, on the speaker portion of the adapter there is an extra black wire, after looking up a diagram for the wiring that wire is labeled as shield circuit 57, should that also be grounded, also on the power connector there is a black circuit 57 and the adapter I have doesn't use that as the ground it uses circuit 694, any advice is appreciated, thanks

 

Is there "whinning" with key on, engine off?

Is the noise there with volume turned down?

If it only "whines" with engine running then shut off engine and unplug the 3 wire connector on alternator, this shuts off the alternator, restart engine and see if "whinning" is gone
If so then AC is leaking from the alternator
If "whinning" is still there then its coming from the spark system, which engine do you have?

There are different fixes for both issues

Not sure what "circuit 57" or "circuit 694" is?

 

After unplugging the alternator the whining went away but there is still a buzz coming out of the speakers. It has a 3.0 engine

 

Just FYI, the issue is the 3rd party unit not the Ranger, whats the Brand and Model number of the new radio, I will see if I can find a wiring diagram?
Is it and all-in-one unit or is there an external amplifier?

Radios build for use in vehicles will have noise filters on their power and ground circuits, but it is an extra expense so.............some do not

If the new radios disconnected wires are indeed Ground wires then that could be the issue, and might get rid of alternator whine, may be the buzz
The Buzz is most likely a "ground loop" caused by poor ground or two separate grounds with one being better that the other

Any wire can be an antenna
A Shield wire protects lower voltage wires(under 2v) from picking up RF(radio frequency) from spark system or local broadcasts, emergency frequencies
The shield is usually a bare wire with or without foil that is wrapped around the wires that need protecting, its the better antenna, and is usually grounded at just one end to prevent "ground loops"
This should only be an issue if you have an external amplifier, the wiring inside the unit should be shielded by the design
If you add external devices, like a backup camera those wires should be shielded


You can get power isolators/filters for the 12volt wires to prevent alternator whine, but shouldn't need to
The Buzz means there is a ground issue and fixing that can eliminate the Buzz and alternator whine as well