Fox Add rear frost to my 93 LX 5.0

Crigano · Dec 6, 2022

Hi. My 1993 LX 5.0 came without the rear defrost option and I’d like to add it.

I know I need a new rear glass with the defrost lines but can someone help me out with what else I need?

Thanks so much!

Mustang5L5 · Dec 7, 2022

The switch, the defrost relay, the rear glass.

As for wiring, you'll have to check if the hatch wiring in your car contains the large gray wire for the defrost circuit. It's hit or miss if the subharnesses on these cars are the sale, or if they are dependant on the options that come with the car.

There's also a large gray wire that will run from the driver's kick panel area, under the door sill area, and up by the rear speaker, where it connects to the hatch wiring harness. You can remove the sill plate and pull up the carpet and see if you see the wire. I believe it's a VERY LARGE gray wire with a yellow stripe and a single plug. It's solitary

Mustang5L5 · Dec 7, 2022

Here's a pic of the main defrsot power wire. The gray 4-pin connector connects in the driver's kick panel, and the black connector connects in the rear speaker area to the hatch harness. This wire runs under the driver's side door sill area

Then there are awires that connect the defrost glass to the hatch harness. These are for an 87-89, but 90-93 would be similar.

To complicate things further, if the hatch harness does not contain the large gray wire for the defrost and you need to swap it, you must find a 92-93 hatch harness to substitute with it, as the rear latch wiring is unique to those years and 87-91 will not work

AeroCoupe · Dec 7, 2022

What if it is a Coupe car?

Mustang5L5 · Dec 7, 2022

AeroCoupe said:
What if it is a Coupe car?

For some reason I thought the original post said GT.

If it's a coupe, same wiring applies until you get to the rear package tray area. Main harness ends and you would just need the coupe specific subharness under the tray.

I'm going to guess since the defrost wiring is it's own specific wiring harness, he's going to need all the wiring from the driver's kick panel back.

The plugs for the defrost relay and the switch are already present.

Crigano · Dec 7, 2022

Mustang5L5 said:
Here's a pic of the main defrsot power wire. The gray 4-pin connector connects in the driver's kick panel, and the black connector connects in the rear speaker area to the hatch harness. This wire runs under the driver's side door sill area

Then there are awires that connect the defrost glass to the hatch harness. These are for an 87-89, but 90-93 would be similar.

To complicate things further, if the hatch harness does not contain the large gray wire for the defrost and you need to swap it, you must find a 92-93 hatch harness to substitute with it, as the rear latch wiring is unique to those years and 87-91 will not work

Amazing! Thank you for this info! I’ll take a look and see what I have.

Crigano · Dec 7, 2022

Mustang5L5 said:
Here's a pic of the main defrsot power wire. The gray 4-pin connector connects in the driver's kick panel, and the black connector connects in the rear speaker area to the hatch harness. This wire runs under the driver's side door sill area

Then there are awires that connect the defrost glass to the hatch harness. These are for an 87-89, but 90-93 would be similar.

To complicate things further, if the hatch harness does not contain the large gray wire for the defrost and you need to swap it, you must find a 92-93 hatch harness to substitute with it, as the rear latch wiring is unique to those years and 87-91 will not work

So, dumb question. If I have the switch relay and wiring all hooked up, I should be able to turn the switch on, check the end of the wire that connects to the glass and, as long as I have power, it should defrost the glass correct?

Mustang5L5 · Dec 7, 2022

Correct. That grey wire to the rear is 12v+. So one side of the grid grounds to the body and the other side gets 12v. The grid lines themselves have resistance, so that generates the heat to warm the glass.

This is a 1988 wiring diagram, so it's not exactly correct for 1993 but it gives you a rough idea on how the glass is wired in

Crigano · Dec 8, 2022

Mustang5L5 said:
The switch, the defrost relay, the rear glass.

As for wiring, you'll have to check if the hatch wiring in your car contains the large gray wire for the defrost circuit. It's hit or miss if the subharnesses on these cars are the sale, or if they are dependant on the options that come with the car.

There's also a large gray wire that will run from the driver's kick panel area, under the door sill area, and up by the rear speaker, where it connects to the hatch wiring harness. You can remove the sill plate and pull up the carpet and see if you see the wire. I believe it's a VERY LARGE gray wire with a yellow stripe and a single plug. It's solitary

So, per the attached pics it doesn’t look like I have the large gray wire that runs from the kick panel to under the sill plate to the rear speaker area. Also, the defrost relay should be mounted under the dash on the drivers side right? If so, do you have a pic and can confirm location?

Thank you!!

Crigano · Dec 8, 2022

Crigano said:
So, per the attached pics it doesn’t look like I have the large gray wire that runs from the kick panel to under the sill plate to the rear speaker area. Also, the defrost relay should be mounted under the dash on the drivers side right? If so, do you have a pic and can confirm location?

Thank you!!

I also have these two plugs free under the dash.

Crigano · Dec 8, 2022

Crigano said:
I also have these two plugs free under the dash.

I also see this gray plug in the back of the hatch if I trace the wire running behind the rear drivers side speaker.

Crigano · Dec 8, 2022

Crigano said:
I also see this gray plug in the back of the hatch if I trace the wire running behind the rear drivers side speaker.

And it looks like the wiring to the switch is already there.

Mustang5L5 · Dec 8, 2022

I think the gray wire is taped into the bundle. Gray wire with yellow stripe. I think I see it in your pics in the back.

Let me pull out my 1993 EVTM later tonight and get some diagrams for you.

Crigano · Dec 8, 2022

Can’t say thanks enough for the help!

Mustang5L5 · Dec 8, 2022

Here are the 1993 specific diagrams

Location of relay. Looks taped up around the fuse box. You should have a brown/lt blue wire on one side from the relay, and a gray wire on the other side.

I see the plug in your picture, but cannot make out wire colors to see if the outgoing gray wire is there.

Here’s the wiring diagrams. C203 is located in the drivers side kick panel and is a 12-pin black connector

Mustang5L5 · Dec 8, 2022

Here’s the relay plug, which matches up to that white plug you posted a pic of earlier

Crigano · Dec 8, 2022

Mustang5L5 said:
Here’s the relay plug, which matches up to that white plug you posted a pic of earlier

This is fantastic! Thank you so much for the diagrams! I’ll take a look tomorrow and will see if I can find the gray/yellow cable in the hatch. Now I just need to find the relay itself lol

Crigano · Dec 9, 2022

Mustang5L5 said:
Here are the 1993 specific diagrams

Location of relay. Looks taped up around the fuse box. You should have a brown/lt blue wire on one side from the relay, and a gray wire on the other side.

I see the plug in your picture, but cannot make out wire colors to see if the outgoing gray wire is there.

Here’s the wiring diagrams. C203 is located in the drivers side kick panel and is a 12-pin black connector

Found the plug in the hatch! I ordered the relay, now will get the switch and the cable that connects from this one to the glass, then the other one that connects to glass and ground.

Can’t say thanks enough for the help. Really thankful and appreciate all the help!

Fox Add rear frost to my 93 LX 5.0

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