Vintage car audio wiring.

[Propflux01]

Have an old late 70’s/early 80’s car stereo/am/fm/cb radio. It nase 4 wires coming off of it. Red, black, grey, brown. The black wire is bolted to a stud on the chassis of the radio. I powered the radio up using the red + and black for - . I am assuming the grey and brown wires are right and left speaker wires. question is, when wiring speakers, should the speaker neg just be grounded to a meta part of the car, or ran back to the black wire on the radio?

 

[Hall]

Have you tried Googling for an owner's manual for the head unit ? There's a possibility that someone has a scanned copy out there. Stereos of that era are before my time frame but years later, I was into car stereos pretty heavily. I've personally never heard of speaking wiring from the head unit that was the "+" wire only but if you just used a short wire from the speaker's "-" terminal to a metal part, that should work. Downside is you are probably going to create "ground loops" (humming noise that follows the engine RPMs). That's why it's always better to use a single ground point.

 

[Propflux01]

Have you tried Googling for an owner's manual for the head unit ? There's a possibility that someone has a scanned copy out there. Stereos of that era are before my time frame but years later, I was into car stereos pretty heavily. I've personally never heard of speaking wiring from the head unit that was the "+" wire only but if you just used a short wire from the speaker's "-" terminal to a metal part, that should work. Downside is you are probably going to create "ground loops" (humming noise that follows the engine RPMs). That's why it's always better to use a single ground point.

Yes, Google fu and no results. I remember the older 4 wire, just couldn’t remember if the speaker neg wires were grounded to chassis or ran back up to the radio and tied in with the black neg wire.

 

[Hermann]

Depends on the type of power output transistors it has. This appears to be a common ground unit. Hook up the speakers neg terminal to any thing metal and it should play. If it were one of my installs from that era I would run speaker wires to the speakers, then wire the negative leads on each speaker would be combined, then hooked to the black wire coming from the unit. From 20 years experience installing in the era that stereo came from.

 

[Propflux01]

Sounds good. Thank you

 

[brianl703]

question is, when wiring speakers, should the speaker neg just be grounded to a meta part of the car, or ran back to the black wire on the radio?

If you think you'll ever replace it with a modern car stereo, you want a separate wire run back to the radio.

Modern car stereos don't use common grounded speakers.

 

[Hermann]

If you think you'll ever replace it with a modern car stereo, you want a separate wire run back to the radio.

Modern car stereos don't use common grounded speakers.

Correct, new wiring never hurts. Only benefits

 

[sk_pete]

Modern car stereos don't use common grounded speakers.

because more oomph from btl

 

[mk378]

you want a separate wire run back to the radio.

Exactly. Run two wires to each speaker, and with this radio ground the minus wire of each speaker at the radio. With other radios both speaker wires are active and must be connected to the radio.