That's actually a good sign so far, but the main damaged wire does not go to or through a fuse, so the only thing able to protect it is the fusible link previously mentioned.
I did move the voltage regulator out of the way to do some inner fender painting, but didn't undo any connections there, other than the ground. What do you mean by replacing the entire circuit, the wire from beginning to end, or does this include all components associated with the wire?
That's a problem.
You should never have your voltage regulator connected when it's un-grounded while the battery is still connected. You can fry your regulator, and then that can cause an over-charge situation. Which may be what started the cascade effect of smoking wire.
Yes, replacing the wire from one end to the other. But this is not a simple task because it has splices and connections to other circuits built in at the factory. It's not just a simple loop, but it can still be done. Just takes more work.
With replacing in mind, you can look for any sections that are not damaged (if such exist) and keep those and splice in new wire where it's needed.
This is not really recommended though, if you keep it working in the same fashion as the factory did it. This would only be advisable I think if you change the loop to a single wire that powers up the vehicle, disconnecting the alternator from the loop and running a new wire directly from the alternator to the battery positive. No more ammeter function, but that can be replaced by a voltmeter instead and you avoid the future potential issues of running all of your power through one wire with multiple splices.
The only way I'd keep it functioning as an ammeter wire is if you replace the entire run with new 10ga wire, and use junction blocks to feed the other circuits instead of splices. Unless you're an expert at wiring and can do perfect splices, the single wire scenario with junction blocks OR the split function scenario where you wire the alternator directly to the battery would be the way to go.
I'll try to get a picture of the damaged wire under the dash too. What's the best way to access the under dash wiring, remove gauge cluster/speedometer?
There's probably only one "best" way I suppose. That's removing the entire dash to work behind it.
However since your '69 has those two firewall connectors you can probably get away with removing the cluster only for access to the key points of the harness.
Removing the driver's air vent is a good thing too, since for just a few screws and cutting through some old gasket and goop, you get even better access. I'd do that first in fact, and you can then see the back of the cluster even while it's still mounted to the dash.
The entire length of wiring was smoking, so I don't think a splice will be an option.
I'd have to agree...
My main battery ground didn't melt, the engine ground to the alternator had the melted insulation. I didn't remove the ground from the engine when I replaced the alternator, just the connection at the alternator.
I'll look at the new pics closer, but there is normally not a ground wire between the alternator and engine. That is done through the physical contact between the two.
The melted wire might be the same Black wire that burned up throughout the harness.
I have the rectangular connectors at the firewall. I'll get a picture of that also. Are these connectors reusable? If not, how do you go about replacing them?
They are serviceable to a point, but if damaged I don't believe they are reusable or fixable. But inspection will tell you the tale. If they are, it won't be an easy task I'm thinking.
Paul