Radio wiring… yikes.

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Joined
Oct 14, 2018
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Location
Clinton Township, MI
My Car
1973 Mach 1 Q Code 351CJ, 4 speed manual, bright red.
2004 Mustang GT Convertible (Mach 1 Tribute)
Got the bright idea to upgrade from the factory(ish) radio and speakers to a retrosound setup. Wiring is far from my strong suit so I finally broke down and bought the wiring manual ebook from ford manuals website. That was somewhat of a help in regards to the speaker wires coming out of the right side of the radio and the blue/red being the light, but not 100% on the rest here. I’m going to take a guess that the black coming in on the left side is the ground, the purple/white is accessory feed and the two yellows that appear to be spliced into the blue/red are 12v feed? Obviously not a factory setup here, Marti Report indicated the car came with AM radio only so one of the previous owners must have gotten ahold of a "factory" AM/FM and did.. well… whatever they did here. :rolleyes: Any help/clarification will be extremely appreciated!FullSizeRender.jpegFullSizeRender.jpegFullSizeRender.jpegFullSizeRender.jpeg
 
I have one important comment. The early AM radio and some FM used a singled ended connection to the speakers. Meaning one side (+) is the actual audio driver , the other may be grounded (-) to the chassis. The newer radios all run a differential signals setup. That means both wires from the speaker (+-) get connected to radio output. The new radio wiring will show this setup.

This just means any the existing wiring may not be totally compatible with the newer radios. Not a big deal ! to add the other signals you may need.
 
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Update! So upon tracing down the yellow wire(s) that appear to be spliced in with the blue/red wire, the wire running off to the left goes directly into the fuse box (looks like constant 12v feed?) and the wire running off to the right goes through the firewall through a corrugated cover, comes out of the cover under the coil and onto the coil terminal.

Forgive my lack of electrical knowledge but what I’m getting here is this yellow wiring from coil to radio to fuse box is the 12V constant feed the new radio is looking for, the white purple wires are the accessory feed, and factory radios grounded at the mounting strap, whereas the new radio requires its own ground. Please correct me if I’m wrong.

Pictures show where I traced the yellow wire to.
Also, yes I know the red/green wires in the plastic with the yellow wire are for a switch ran for aftermarket fog lights under the front bumper.IMG_6014.jpegIMG_6015.jpegIMG_6013.jpegIMG_6023.jpegIMG_6022.jpeg
 

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I have one important comment. The early AM radio and some FM used a singled ended connection to the speakers. Meaning one side (+) is the actual audio driver , the other may be grounded (-) to the chassis. The newer radios all run a differential signals setup. That means both wires from the speaker (+-) get connected to radio output. The new radio wiring will show this setup.

This just means any the existing wiring may not be totally compatible with the newer radios. Not a big deal ! to add the other signals you may need.
As far as the speaker wire that’s easy, what’s existing is being taken out and new wire provided with new speakers are going in, speakers and radio are all the same brand so wire gauge is a perfect matchup. Figuring out the constant 12v feed and accessory feed was my dilemma.
 
Ha ok. It can be really really tough to unscramble someone else wiring even with electrical know how !!!!

Seems if a bunch of modifications have been made. Normally the radio chassis does get it's own ground The older radios used a metal post to mount to car. Your picture shows that. Newer radios provide that separate wire you mention that you will need to ground. Try to ground as close to the radio as possible. I guess the new resto mod radio requires a constant ,12 VDC and the 'accessory' line you mentioned is what turns the radio on and off. This is a switched line that would normally supply power when the ignition is on or in accessory mode.

TonyD
 
Well I’ve finally figured out the existing wiring headache. I traced all the yellow wires to one source… my aftermarket tach that grandpa installed when he had it. Rather than keeping the color coding of the wires coming out of it he must have had an over abundance of yellow wire to use up at the time. Coming out of the tach, red goes to yellow which goes to the fuse box, green goes to yellow which goes to the coil, black goes to yellow that is grounded for dash structure. Now the fun one that took me long enough to figure out but now makes sense, the blue wire from the tach that powers the light in it is spliced into the blue/red wire for the radio light, also my aftermarket temp/oil/amp gauges have a yellow wire coming down from them that is also spliced(and soldered) to the red/blue wire. So he used the radio light power wire to power the rest of the non cluster gauge lights.

So, the only thing I have yet to figure out is, the wire coming out of the fuse box for the tach’s power, is it a switched 12V or a constant 12V? If it’s not a constant 12V feed, where(and how) in the fuse box can I tap into 12V constant power?IMG_6061.jpeg
 
The yellow wire (and orange one) appears to be from an unfused switched power source. I recommend installing an inline fuse or switching them to a fused source. The fuse next to them feeds the wire/purple stripe wire which also provides switched power to the radio.
The two fuses on the right side of your photo are both constant power, the 20 amp fuse feeds a yellow with blue dots wire to the horns and a light blue with white stripe wire that runs to the lighter. The 14 amp fuse feeds a light green with yellow stripe wire that runs to interior lights and clock.

Post #3 in this thread has a how-to guide for reading wiring diagrams, which may help you.
https://7173mustangs.com/threads/how-to-read-wiring-diagrams.40106/#post-413573
 

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