Troubleshooting '68 Mustang: Hot Wiring and Checking Ignition System

[Averagesupernova]

Yes the external shunt is what you are looking for. Why are you dragging a new diagram into this? The diagram in this link:
http://mustangforums.com/forum/classic-mustangs/596726-amp-gauge-wiring.html
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shows it just fine. In fact it is in better detail. If this wire #37 is intact you will have power at the large terminal on the alternator even with the connectors on the firewall unhooked. This is where you need to be looking. I don't know what color it is in real life. I know it has to carry complete charging current so I would say back in the day with the size charging system that car had possibly a #8 wire.
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Edit: Do you have a reason to believe the diagram in the link I gave is inaccurate?

 

[Big Block]

Averagesupernova,
Had work I had to attend to. This is the status so far.

I have completely rebuilt the alternator wiring harness-brand new (including the shunt). I have power to both sides of the ammeter (unlike in posts #12 and #17). Also, I have power to the large lug (#37) at the alternator (reference post #60).

Although I did check the ignition switch wiring with a continuity check their was 1 female pin hole (B, for #37) that was brown around the edge. So, I'm buying a new ignition switch wiring harness-just to be safe...

BTW, how does one place a picture in the left-most margin under your name "Big Block"?...

P.S. The wiring diagrams are just fine, but the wire color codes are different.

 

[Averagesupernova]

Ok so you have replaced a significant part of the wiring in question. What specifically is not working on your car now?

 

[Big Block]

Averagesupernova,
So, I'm buying a new ignition switch wiring harness-just to be safe...

BTW, how does one place a picture in the left-most margin under your name "Big Block"?...

P.S. The wiring diagrams are just fine, but the wire color codes are different.

Results = No power:
. at the ignition switch (or cranking)
. no courtesy kights
. no radio
. no instrument panel lights
. no parking or headlights

 

[Averagesupernova]

Start at the connector on the firewall from the outside. Verify you have power on the pins you believe you are supposed to. Then go inside and do the same thing. There is most likely just ONE connection that is open. The test from the outside to the inside should show this up.
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Refer to the diagram I linked in post #61. There is a node of 4 wires next to the firewall connector coming together in which one of them is #37 shunt hi-lighted yellow. The wire that goes through the connector and is labeled 37 which then goes off the diagram is most likely the one you need to follow.