Stereo receiver power wire

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n_reckless

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I just installed a stereo system with an amp and a receiver. Someone has swapped the factory receiver around the '70s to an aftermarket unit with 3 wire connection. I hooked up the new receiver and has no power. I don't have experience with electronics but my first thought is to hook up the receivers power wire to the fuse of the amps power wire. Should it work that way? I attached a photo about my idea. 

 

Don C

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Does the receiver have a key on connection also, to turn it on and off? If so, that fused power wire should work fine. By 3 wire I assume it is key on source, main power feed, and antenna.

 

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Does the receiver have a key on connection also, to turn it on and off? If so, that fused power wire should work fine. By 3 wire I assume it is key on source, main power feed, and antenna.
The new unit is a USA-630 from Classic Car stereos. It has only one power wire for switched 12v and a yellow for the memory. 

in this case should a splice in the amps fused power wire would work?

 

Don C

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It will work fine for the memory. Do the instructions specify a fuse size for the memory wire? The fuse for the amp may be larger and you may want to install a smaller fuse after the amp fuse for the memory wire.

 

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The biggest problem with the amp's blue wire hooked up to constant power is that it will eventually drain the battery, since the amp will always be 'on' regardless of whether the stereo is or not.  I'm surprised the USA-630 doesn't have a lead for 'remote' power (power antenna - should be blue, which is commonly used for the amp's 'on/off' circuit).

 

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The biggest problem with the amp's blue wire hooked up to constant power is that it will eventually drain the battery, since the amp will always be 'on' regardless of whether the stereo is or not.  I'm surprised the USA-630 doesn't have a lead for 'remote' power (power antenna - should be blue, which is commonly useid for the amp's 'on/off' circuit).
The usa 630 has a remote wire. I'm asking about the main power (red) wire. If I can hook it up to together with the amps wire.

 

Don C

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You'll have to remember to turn the stereo off every time you turn the engine off, or you'll be powering the receiver and amps from the battery without the alternator supplying power, which will run the battery down in a few hours. You should power the red wire with a power source that is turned on and off with the ignition key. The yellow memory wire will be fine connected to the wire powering the amps.

 

n_reckless

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You'll have to remember to turn the stereo off every time you turn the engine off, or you'll be powering the receiver and amps from the battery without the alternator supplying power, which will run the battery down in a few hours. You should power the red wire with a power source that is turned on and off with the ignition key. The yellow memory wire will be fine connected to the wire powering the amps.
So the wire for the yellow/memory/constant 12v is ok to be connected together with the amps power wire. And if the remote is also hooked up I only need to connect the red/switched 12v to power the stereo. Is the ignition on the solenoid is a good place to connect it? If not what would be the best way to connect the switched 12v?

 

Don C

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No, the ignition wire "S" on the solenoid is only hot when you crank the engine. The "I" wire has 12 volts only when the engine is being cranked, the rest of the time, when the engine is running, it only has around 8 or 9 volts, being fed by the resistor wire to the coil.

Your best bet is to find the original radio power and illumination wiring under the dash. The radio you took out may have been connected to them. The power wire to the original radio is white with a purple stripe and provides power when the ignition key is in the run and accessories positions. The dash illumination wire is light blue with a red stripe and has the dimming feature the rest of the dash illumination lights have. Originally they were both terminated in a connector the original radio connected to and would be near the radio location.

 

n_reckless

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No, the ignition wire "S" on the solenoid is only hot when you crank the engine. The "I" wire has 12 volts only when the engine is being cranked, the rest of the time, when the engine is running, it only has around 8 or 9 volts, being fed by the resistor wire to the coil.

Your best bet is to find the original radio power and illumination wiring under the dash. The radio you took out may have been connected to them. The power wire to the original radio is white with a purple stripe and provides power when the ignition key is in the run and accessories positions. The dash illumination wire is light blue with a red stripe and has the dimming feature the rest of the dash illumination lights have. Originally they were both terminated in a connector the original radio connected to and would be near the radio location.
Thanks, and happy new year!

That was my second thought. And what about if I already hooked up a relay for solid 12V for an MSD dizzy?

 

Don C

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What did you use for the trigger wire for the relay?

 

Don C

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If you used the Pertronix relay it should be fine. Other 12 volt relays are designed to work on 12 volts, not the reduced voltage of the coil wire or the "I" terminal. When you crank the engine a regular 12 volt relay will engage, but may not stay engaged on the reduced run voltage. In order for the relay coil windings to continue to work it will draw more current at the reduced voltage, which may damage the windings in a regular 12 volt relay.

https://pertronix.com/pertronix-2001-ignition-power-relay-kit.html#product_tabs_description_tabbed

EDIT: The above is assuming that the original ignition wiring is still in place and the circuit that connects the coil to the "I" terminal is still active.

 
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n_reckless

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If you used the Pertronix relay it should be fine. Other 12 volt relays are designed to work on 12 volts, not the reduced voltage of the coil wire or the "I" terminal. When you crank the engine a regular 12 volt relay will engage, but may not stay engaged on the reduced run voltage. In order for the relay coil windings to continue to work it will draw more current at the reduced voltage, which may damage the windings in a regular 12 volt relay.

https://pertronix.com/pertronix-2001-ignition-power-relay-kit.html#product_tabs_description_tabbed

EDIT: The above is assuming that the original ignition wiring is still in place and the circuit that connects the coil to the "I" terminal is still active.
Yes, I'm using the Pertronix relay but my ignition wire is disconnected.

 

Don C

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Sounds like your ignition is good to go, then. My only question about it is what coil you're running and is it connected to the original coil wire. If so you may be able to improve your cold starts by connecting the wire to the "I" terminal to supply battery voltage to the coil while cranking the engine.

Did you find a suitable source for your receiver main power?

 

n_reckless

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Sounds like your ignition is good to go, then. My only question about it is what coil you're running and is it connected to the original coil wire. If so you may be able to improve your cold starts by connecting the wire to the "I" terminal to supply battery voltage to the coil while cranking the engine.

Did you find a suitable source for your receiver main power?
I'm running an MSD Blaster II with a ready to run dizzy. I need to check if the original wire is still connected but I don't think so.

Hell, I haven't find a main power yet. Since November I'm working straight and my only day off was Christmas Day when I was able to install the amp, speakers and the receiver and my next probably will be around March when we'll finish our project and It's still getting dark early to do it when I get home.  That's why I'm asking a lot and want to make sure I'd good to go hooking it up because it'd take only 10 mins and I could do it during lunch. :D

 
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