Ammeter to Voltmeter conversion

There were two  wires I just couldn't figure out in the under-dash harness, and they were different from the rest in that they were much heavier gauge.  They also looked like they could connect to each other, but I didn't understand why they would have not just made a single wire if that were the case.  The picture below points them out:

They were not included in the wiring book I had, so I finally took the wiring harness to my local parts guy, who is a real expert in vintage Mustangs.  He immediately identified the wiring harness as a 65 GT harness, and the wires in question were for the ammeter.  The base Mustang had an idiot lite to show charge, and it was the GT that had an actual ammeter gauge in the 65 model year.  The way it worked is that these two wires were plugged together and carried the full output of the alternator past a sensor in the ammeter that measured amps by the force of the electrical field in the wire.  In 66, they did away with this method and used a "shunt" to reduce the current so that the wires could be connected directly to the ammeter.  Since we had a 66 gauge cluster, that meant the ammeter could not be used.  Hooking the two wires in the 65 harness above to the 66 ammeter would have caused melting of the instrument panel and perhaps a fire.  After some online research I decided to convert the ammeter to a voltmeter.  This actually is better than an ammeter as it shows the status of the battery, which will loose charge if the alternator is not outputting current, and will show an overcharged condition if the voltage regulator is not regulating flow from the alternator to the battery.  I bought a voltmeter from Autozone and gutted it for the working parts.  Here is how it looks:

I think I may make a further modification and black out the "Sunpro" brand barely visible at the top of the gauge.  The back of the gauge is a simple hook-up to a 12 volt source from the battery:

Note the new look of my blog.  My friend Mike has started a blog using the same Google program and, being the computer whiz he is, has figured out how to change the template and photo size.  (My daughter Karen set it up for me originally so I didn't learn to do it myself.)