Electrical 91 hatch wiring help needed

[FastDriver]

Even though they're both 1991 hatches the wires are different, and the connectors are too. I probably need to just probe this out, but its good technical fodder for future reference, and hopefully someone can just set me straight @Mustang5L5

Car side

So on Car side:
1. Double LG/Yellow
2. Red/LB (maybe LG)
3. purple/yellow

4.Grey/Yellow (thick)

5. double brown

Hatch side

1. Grey/Yellow
2. Red/LG (LB?)
3. Black

4. Purple/Yellow
5. LG
6. Brown

Also, on the hatch that came out, there were only 5 wires. So, not sure why I have an extra now.

Without probing:
grey/yellow is for defrost power. It's both the same color on each side & thicker than the rest on both sides.

Purple/green: I think this is the hatch popper, saw that in one of the wiring diagrams and there's a purple green on each side.

Red/LG to red: I think this is the third brake light, as I prematurely plugged in the connector that fit and tested it. And I saw something in one of the wiring diagrams

On the car side, that leaves me double LG/Yellow & Double Brown to figure out.

On the hatch side, I still have black, LG, and brown unmatched.

I know I should see the license plate running lights, and maybe something extra for the defrost?

 

[Mustang5L5]

I went through this a couple years ago.

The hatch latch changed in 1991. Early cars had the older style that ran from '79?? thru early 91 and then there was a late 91-93 style. The wiring changed as well because Ford moved the courtesy interior light switch from being mounted near the striker, to being physically part of the latch. So hence that's why you have extra wiring. That harness witht he extra wires is likely for the later style latch.

Grey/Yellow is defrost power

red/green is brake lights

Purple/Yellow is hatch release

Light Green/yellow is one wire for the rear courtesy light switch. The other is listed as black/light blue.


It's been some years since i've messed with this. Unsure if i posted any info when I did i'll have to look


EDIT: some info, but not much

https://stangnet.com/mustang-forums/direct-messages/power-hatch-latch.318397/#convMessage-401788

 

[FastDriver]

Mike, appreciate the input. Your post came in right about the same time I was out in the garage testing and helped confirm what I was seeing.

Here’s where everything landed:
Wires / Functions

• Purple/Yellow: Hatch latch switched 12V trigger
• Brown: License plate lights parking lamp circuit
• Red/Green: 3rd brake light
• Gray/Yellow: Rear defrost 12V feed

Extra Wires

• Light Green/Yellow and Black/Light Blue
  • Courtesy switch integrated into later latch not used on early setup (per Mike)
• Double Green/Yellow car side
  • Constant hot present at hatch
  • Not used on original hatch
  • Planning to run a 12 gauge lead from this into the interior beyond the quarter panel for possible future use such as a nitrous bottle opener

Summary
All functions accounted for:

• Latch
• Plate lights
• 3rd brake light
• Defrost

Extra wiring is due to differences between early and late latch and courtesy switch setups.

Takeaway

Once you separate the required circuits from the extra provision wiring the swap is straightforward.