Hi All,
I have just acquired a nice Audiovox FO-FDXH am/fm radio to replace the modern pos Sony unit in the 80 step-side.
This radio (as I'm told) was a common dealer upgrade and came out of a 79 Mercury.
I'm looking for help to identify the wiring coming from the back of this radio so I can properly mate it to the factory
wiring.
These are the wires:
White x 1
Red x 1
Yellow x 1
Black x 2
Blue x 2
My assumption is that the Black and the Blue wires are for the L and R speakers - the Yellow wire is the 12 v switched power - leaving either the Red or White wire to power the
illumination and the remainder of the two as unidentified.
There is a LOT of guesswork out there about aftermarket stereo wiring but nothing I can find specific to this Audiovox model number.
All help is as always greatly appreciated!

Example photo of Audiovox FO-FDXH AM/FM radio unit.

 

Are all the wires the same guage? Since it's FM I'm assuming it's stereo speakers. Usually black is a ground.

 

I can't any definitive diagram for that radio. I would pull the covers off of it.

You should see a section of the circuit board that has a aluminum heat sink to it. That is the output amplifier that drives the speakers. See which wires lead to there. You may find the black wires are tied together inside the radio, that would mean they are the common ground for the speakers. If some of the wires go up to the **** on the right side of the radio, that means this radio had a front and back fader, and the speaker wires come from the fader control.

One of the wires should lead up to the light bulb behind the dial. That will be for illumination and can go to the lightblue/red wire on your truck's harness.

One of the wires may lead up to the left side ****, this is most likely the power wire. Or one of the wires leads to the circuit board that this will lead up to the left side ****, where you can turn the radio on and off.

This radio probably does not have a ground wire, it grounded through the case of the radio. You may want to bolt a wire to the case to make it a ground wire. You could most likely use the black speaker grounds as a ground, but I wouldn't. It will also tend to ground through the antenna wire, but I would make a dedicated ground to the case of the radio.

 

Being there are 2 blues and 2 blacks I would say they are for speakers.
Now low voltage like a 12 volts on autos use white for ground, look at trailer light wiring were its ground is white.
Now do check before saying the white is ground but just keep that in mind but the radio body could also be the ground.
Maybe the wiring routing is on the inside of the cover?
Dave ----

 

Great tips everyone.
Yes, I have had the cover off of the unit to clean the boards and will do it again to check if the black or
blue are coming off of a heat sink, (thank you Franklin2!) which one runs to the illuminate bulb and of the remaining two try to figure out
which one is the 12v supply and what the other may be. (Possibly for a power antennae since the on/off volume ****
will pull out and in with an audible click.)
Yeah, I'm fairly sure that the unit does ground to the dash frame so the ground wires would run from the speakers back to the unit
and ground through it..
Looks as though I'm going to be brushing up on my Ohms Law, setting it up on a bench with speakers, and grabbing my multi meter.
Would there be any risk of testing it at say @ 9V or should I supply a full 12v?
Thanks!

 

Can't help with the Audiovox details, but the truck's wiring diagrams may help match up the wiring:

https://www.garysgaragemahal.com/1980-evtm.html

See page 51 for the factory stereo and page 38 for the dial illumination.

 

Using a 9v battery may lessen the chances of letting the smoke out.

 

If I remember correctly, speakers always have their own ground wires and never the body of the car / truck or body of the radio because it can pick up EMF noise and why the 2 black wires to go with the 2 blue wires.
1 set of wires most likely has other marks as you would want to pair 1 set black / blue together and the other set together but they are left / right and why they are paired.
Dave ----

edit:
I just tried AI and forget using it for wiring as it list only the
white as the left (+) speaker, no other speakers listed.
Said to tie the 2 black together as they are the ground. Why 2 and not 1 wire?
Red switched power
Yellow power all the time for memory?
Blue power ANT or AMP Also why 2 wires?

So IA failed for this info in my book

 

Thank you Karl,
This will definitely help when I go to remove/replace the Sony CD player in there now.
My shop manual has some helpful illustrations, but no schematics.
I appreciate this!

 

In my experience AI fails more often than not - it still has a loooong way to go...

 

So far this is the first time MS Copilot has failed me but I also dont trust it 100% without more checking.
But that wiring did not make sense for that radio and options.
Good luck
Dave ----

 

I use the google AI once in awhile and it shows it's sources of information. Guess what? On car troubleshooting, it gets a lot of it's information from boards just like this one, and we all know it's not exactly the right info sometimes.

 

I just went back and checked and this is the first time it has not given a source
But you are right it has given the sources other times I asked questions.
The last was for a capacitor for a Emerson 220v 5hp single phase 3450 RPM motor for my son's air compressor as it was missing the capacitor when he got it.
It gave I thought some good information but he is digging deeper to make sure it is right.
Dave ----