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Full 1968 Mustang rewire.

4K views 14 replies 3 participants last post by  Pmustang 
#1 ·
Hello Folks, Hopefully you can help

I am completely rewiring my 1968 Mustang fastback, What complicates matters is that the car is now a 1967 GT350 replica with some aftermarket stuff.

Basically the harnesses in the car are all original as far as I can tell. The initial reason for the removal and replacement was due to the fact the wiring in the car showed some scary signs of deterioration and very poor repairs. The second reason was to install a tach dash harness setup in the car. Upon removal of the headlight harness I saw evidence that proved this was the best course of action, to remove and replace everything.

The car is fitted with aftermarket air which is staying
A 5 speed which is staying
A horrid custom autosound radio setup, which although nearly new doesn't work, surprise surprise which is going and a factory AM/FM will replace
An autometer guage pod setup. Which is going and a factory tach dash is going in its place
Shelby non sequential rear lights. Which are staying
Electronic under the cap ignition which is staying

Okay, so what I am doing is going back to a factory AM/FM and a factory tach dash and leaving everything else.

I spent today removing the headlight harness. This went very well and the new harness from NPD is in place and everything appears factory. I am only in need of a location to attach the ground for the headlights, the old harness was missing this.
I also installed the alternator harness which came out great and everything looks factory
I am working on gauge harness but that will take a bit longer as the Autometer senders need to be swapped for factory ones.

After the headlight harness I started removing the main dash harness. This is taking tons of time as I am teasing out the A/C wiring and verifying what is to go and what is to stay. I don't like to just remove stuff, Even if its going I like to see what it was previously doing.

I did happen to notice at the firewall a connector in the middle of the upper portion of the firewall with a four position plug and I was a bit stumped as to what this was for. Near this connector is the thin triple plug that I assume the gauge feed harness attaches to. After looking at the wiring diagrams online I saw this four position plug must be for an automatic car (which mine originally was as I have the marti report) and for the neutral safety switch (which mine no longer has due to being a five speed) The thing is that on my car there are four wires (non factory) attached to this plug with bullet connectors. So I got to thinking, What connections would there be on a T5 conversion that need to be made? I assume reverse lights and nothing else I could think of.

Can anyone shed any light on what these four wires could be? They come out of the top of the tranmission and run up to this four position square plug in the upper portion of the firewall on the engine side.

Cheers. Peter
 
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#2 ·
This is the plug in question

The square one, I am fairly certain the narrow one partially shown is for the gauge feed

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I can't for the life of me remember the wiring requirements of the T5 in a classic. The fact this is the third one I've had in the car makes that fact even more embarrassing.

Peter
 
#4 · (Edited)
Thanks Pete

Looks like you have a triple flat plug (assume thats for the gauge feed) which I have

Your other plug looks like a four connection like the one i also have.

I have a 68 at the shop I will look over tomorrow.

I will look for T5 wiring mod info and see if my main harness on order from midlife will need the NSS bypass mod.

Cheers. Peter
 
#6 ·
Randy at midlife who has been a godsend on questions like these sent me this

"There should be two black/red wires (backup lights) and two red/blue wires (NSS) coming out of the firewall. That plug is there regardless of manual or automagic tranny. You simply need to jumper the male and female red/blue wires for a manual tranny. The two black/red wires go to the tranny reverse switch. The wire that mates with the female side of the plug out of the fire wall will be hot, although most switches don’t care about polarity"

He also assisted greatly in determining what harness was in my car as I was going tach dash and wanted to know if my car had engine side wiring that was tach ready

CHEERS. PETER
 
#7 · (Edited)
I am completely rewiring my 1968 Mustang fastback, What complicates matters is that the car is now a 1967 GT350 replica with some aftermarket stuff.
Have you considered simply replacing the wiring with a complete 67 GT350 wiring harness? That would solve all your year/incompatibility problems, then you have only to deal with whatever might be bogus about the "aftermarket stuff".

A 5 speed which is staying
There is an excellent adapter wire which connects this to the OEM wiring as if it were factory installed
A horrid custom autosound radio setup, which although nearly new doesn't work, surprise surprise which is going and a factory AM/FM will replace
The CA can be connected as though factory, too

An autometer guage pod setup. Which is going and a factory tach dash is going in its place
The OEM wiring will certainly work with that
Shelby non sequential rear lights. Which are staying
Shelby OEM wiring will work with that, too
Electronic under the cap ignition which is staying
Which also works perfectly with the OEM wiring.

I don't see a problem here.
 
#8 · (Edited)
Hello 22

There are no problems only a few questions

I was not at my shop to view my other 68 fastback and now that I have things make perfect sense. I also didn't have the midlife harness yet to compare main harnesses

Sounds like the T5 harness you mention is the ticket to this issue. Do you have a link to purchase?

I have a Tony Branda Shelby harness specifically for clone cars coming to me to do the taillights. I am using my Factory dash to trunk harness as it was in decent shape.

I went with a midlife 68 harness as that was what was in the car and and after speaking with midlife that was the year of engine harness I had with 68 specific fittings to the brake splitter as well.

As mentioned. The NPD supplied engine harnesses went in smashingly and I hope the main dash one goes in as easily as others I have done.
 
G
#9 · (Edited)
The NSS and backup lights are in a 4 wire plug. For a manual trans, two of them get jumpered together. The other two continue to the trans for the reverse light switch.
Then the other two wires in that location are for the temp and oil pressure gauges.

You can see the 4 wires in that plug ( NSS and Rev lights ) in this diagram.

 
#13 ·
As a sidenote. Must be nice for you US folks to not pay $22 shipping on a $50 part. Plus when it arrives a week or so later pay import fees, taxes and brokerage fees. Not having a moan about CJ. It is what it is. Just lets you know how much us UK folks love mustangs to suffer the additional pain.

That's why I research the heck out of parts needed before purchase. :).
 
#15 ·
Being an expat I know it both ways

My monthly parts spend is high enough that I buy most standard needed stuff in bulk and ship consolidated by container but obviously I get caught short sometimes when I run out or when doing non typical repairs

Peter
 
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