Interior and Upholstery 1990 Mustang constant hot to radio (premium sound)

90Hatchback

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Oct 30, 2018
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California, United States
I'm preparing to install a new radio in my 1990 hatchback. I have a new head unit and new door speakers. There are no dash speakers and the rear speakers are present but untested. The doors have speakers, but are also untested.
I've pulled the amp from behind the radio and have also pulled the amp's 6-connector wiring harness. I'm left with two 8-wire connectors, a black one and a grey one. I'm guessing, grabbing a basic radio installation harness is all I need? Said new harness should connect to the two previously mentioned black and grey connectors and wired to the connectors that came with the radio?

My main questions are:
my electrical troubleshooting manual shows the constant hot wire to the radio harness is light green/yellow, but I'm not getting any signs of life when I probe that wire (piercing the wire, and checking both ends of the connector). The manual shows that the light green/yellow wire goes to the fuse panel and is hot at all times. But, where does it actually connect at the fuse panel? All of the fuses that are supposed to be hot at all times are correctly hot. So, if that is the case, should I expect an open circuit somewhere between the fuse panel and the radio (i.e. cut wire or bad connection) or is there something easier to look for first?
I'm not seeing any signs of life through the switched yellow/black wire when the key is in the on/run position either.
The light green/yellow wire has a 54 next to the wire in the wiring diagram...what does that tell me?
The yellow/black has a 137 next to the wire in the wiring diagram. I believe this wire to be the wire connected to the radio fuse in location #11 in the fuse box.
 
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90Hatchback

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Oct 30, 2018
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California, United States
1990 Ford Mustang Radio (premium sound) schematics
 

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Mustang5L5

i'm familiar with penetration
Mod Dude
Feb 18, 2001
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Wire 54 goes to fuse position 8 that is hot at all times.

Look at page 12-3 and 12-4. Splice 200 is probably what you want to find as it's where the radio got splits from the glove box and instrument lights. Are any of the items on wire 54 not working?

Page 152-13 indicates where s200 is located
 

90Hatchback

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Oct 30, 2018
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California, United States
@Mustang5L5 You are the man!
Glove box lamp - does not appear to be working...but I have never checked it's bulb.
Instrument panel dimming control - instrument panel dims when I rotate the knob.
Engine compartment lamp
- no bulb installed **EDIT** going with not hot here - probed c102 and the lights connector with a light.
Left front courtesy lamp switch - not sure where this switch is located. I don't think any courtesy lamps work, other than the dome light.
Power mirror switch - works perfectly.
Vanity mirror lamp
- neither work, but I'm not sure they're connected (never checked)
Map lamp - has sunroof (so no map lamp)
Right front courtesy lamp switch - same as above (are these the door triggers? Door triggers work fine.)

I'll look for splice 200! Will also check the glove box lamp, and mirror lamps tomorrow.

EDIT:
The front courtesy lamp switches ARE, in fact, in the front door jambs and turn the interior lights on and off when the door is open and shut (pg 151-3).
 
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90Hatchback

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Oct 30, 2018
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California, United States
BTW, I literally ordered the vacuum and electrical troublshooting book last week and have only had it for 2 days. I haven't even flipped through the whole thing yet. Simply directing me to the proper pages has really helped me figure out the layout of the book.
 

90Hatchback

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Oct 30, 2018
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OK...Be careful what you read!

While working inside the car, I didn't want to drain the battery by having the doors open for so long (I have a weak battery that's getting replaced this weekend). So, I looked up a fuse panel diagram and found one that was supposed to be for the 1990 Mustang. So, I printed it off AND laminated it. In referencing that sheet, it said the courtesy lamps were on circuit #8, with the key warning chime, fuel filler door, glove box lamp, clock and power windows. So, I pulled that fuse.
I never stopped to think, the key chime still chimes, and the windows still work.
So, when checking the items that were on circuit #8 from the Vacuum and Wiring Troubleshooting diagram, it didn't dawn on me that I assumed the radio was on circuit #11 (which has a fuse) instead of #8 (which had no fuse). When testing each item, it still didn't register to me that the radio shouldn't be on the same circuit as some of this stuff ACCORDING TO MY INCORRECT DIAGRAM. Some of the things I knew to be working, I didn't actually verify that it was currently working. Had I done that, I would have realized I was working on a different circuit than I thought I was. When reading the book from back to front today, the problem made itself known.
I put a fuse in circuit #8 and everything on that circuit is now hot...even the radio.

**EDIT**
Correct 1990 Mustang fuse panel diagram attached.

Problem now, when I plugged the radio in, it didn't work. I only plugged in the power connector, and not the speaker connector. Would that keep the radio from working?
 

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90Hatchback

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Wired the front door speakers, turned the radio on and actually had good reception in my garage. All appears to be working. I'll pull the plug and attach the rear speakers. Once they all work, I'll solder all the connections and be done.
There is a random black and black/white wire coming to the passenger side under the carpet. I think that is going to the rear speaker. I think I saw one on the drivers side a while back. So, guessing those are for the rear speakers. I'll open the rears and see what's up there before proceeding.
 

Chieftain

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Sep 29, 2018
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If your old radio is working as should, are you interested in selling? I have a 90 LX premium sound with a high dollar aftermarket Alpine. I want to put the original type back in. Thanks
 

WillWho?

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The fun of wiring the radio. You can add dash speakers, they run off of the same color wires as the door speakers. Crutchfield is a good resource for fitment.

There are 2 types of radio connectors in EVERY fox body. Premium radio, which has the amp and speakers in the door and dash and standard radio with door speakers and rear speakers.

The extra set of connectors is taped to the bundle of radio wires back where it splits off of the main harness. It is usually completely covered in tape.

The wire from fuse 8 is for the clock in the radio and retains the memory functions for the station assignment of the buttons. This is a Light Green/Yellow wire.

Fuse 11 provides the on/off and powers the radio, amp, and equalizer when installed, all via a Yellow/Black wire.

Fuse 6 controls the illumination of the clock when the ignition is in ACCESSORY/RUN and Headlight Switch in OFF, it passes 12V to the illumination relay on the White/Purple wire. The relay is not energized, so the 12V passes straight through the relay and sends 12V to the radio display on the Orange/Black wire. This makes the clock very bright to compensate for daylight.

With the ignition in ACCESSORY/RUN and Headlight Switch in PARK/HEAD, it routes 12V from the HLS (powered by fuse 4) on a Brown wire to: parking lights, light chime, the illumination relay, and the Dimmer Control Switch. The DCS connects to the illumination relay and the radio on the Light Blue/Red wires. (The absence of voltage on the Light Blue/Red wire tells a logic circuit embedded in the radio to use full illumination.)

The Brown wire energizes the illumination relay, causing the relay to switch input from the fuse 6 12V to the DCS variable voltage output. That variable voltage goes through the relay and passes the variable voltage to the radio display on the Orange/Black wire. This allows control of radio display brightness through the DCS.

Here is a diagram that I use. It is quite helpful.
20190202_091425.png
 
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90Hatchback

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Does anyone know where the wires to the rear speakers run? It looks to me like they run behind the instrument cluster, down to the drivers kick panel and into the large group of wires that runs at the base of the drivers door to the rear quarter panel. If that's the case, how do the wires get to the passenger side rear speaker wire? Is it run under the back seat, or behind them???
 

WillWho?

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Does anyone know where the wires to the rear speakers run? It looks to me like they run behind the instrument cluster, down to the drivers kick panel and into the large group of wires that runs at the base of the drivers door to the rear quarter panel. If that's the case, how do the wires get to the passenger side rear speaker wire? Is it run under the back seat, or behind them???

The bundle runs under the lower door sill, behind the rear interior panel, up over the wheel well. Then left rear speaker bundle splits off at about the 12:30. Then at the 2:00 there are two connectors that split from the main bundle: one for defrost and one that connects to the center mount stop lamp, hatch release, and tag lights. That bundle goes to the top of the roof to meet the hatch and passes through a rubber boot/ sleeve. The right rear speakers continue through the main bundle all the way to the back of the car, crosses all the way to the passenger side, continues behind the plastic trim all the way to where the speaker is mounted.

On 2-doors, the right speaker has the bundle split off and run beside the wall along the backseat. Too many pinch points to do that in a hatch.

Here is a pic of the connectors for the radio and premium.

20181211_144343.jpg
 
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90Hatchback

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Wow...by "all the way to the back of the car, crosses all the way to the passenger side " you mean the passenger rear speaker wire runs from the drivers side to the passenger side back by the license plate and then forward on the passenger side from the rear tail light area to the rear seats and up the trim there???
 

WillWho?

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Wow...by "all the way to the back of the car, crosses all the way to the passenger side " you mean the passenger rear speaker wire runs from the drivers side to the passenger side back by the license plate and then forward on the passenger side from the rear tail light area to the rear seats and up the trim there???

Yup. That is what my EVTM shows. I barely remember doing the speaker wires in my 89 back in the latter part of the 90's. That is why I had to pull out the EVTM.
 

90Hatchback

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Oct 30, 2018
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California, United States
Where does the EVTM show the routing back there? I was looking for it, but couldn't find it.
BTW, I don't have any wires next to the right rear fender well. So, who knows what the previous owner did with those wires.