1976 Highboy; ammeter dances at idle, then pegs at anything higher than idle.

A few days ago I noticed that the ammeter in my pickup was dancing around, and would "peg" if I increased the engine speed to anything above idle. I immediately thought a short existed so I tested all the battery connections and removed everything aftermarket (brake controller, spare battery connections etc...) and tested the connections to see if there was any current flowing through the wires where it shouldn't... while I was doing this, I noticed that the yellow wire coming from the alternator to the voltage regulator was melted... thinking it'd most likely come in contact with the headers, I repaired the wire and re-wrapped the harness. I fired it up, noticed the ammeter was still dancing, then noticed that the wire I'd just repaired had started to melt again.
I just went through the majority of the harness chasing an issue about a month ago and inspected all the wiring, so I'm thinking the odds of a short existing are nil.
I did a quick search here and found a few posts vaguely similar which made it sound like the voltage reg or the battery could be bad. the battery is a 1.5 year old optima redtop so I'm doubtful that it's gone south this soon. Is a bad voltage regulator the most likely scenario, or does a short somewhere seem more likely to be the culprit?
Thanks.

 

Maybe it is actually a volt meter and the external voltage regulator is bad? That's my first thought if the wires are melting.

 

Is this a factory ammeter or an add on aftermarket ammeter?

 

it's the factory one in the dash. I'm headed to the parts store to grab a new voltage regulator, hopefully that'll fix it

 

As you suspect, usually a sign voltage is not regulated. If you can put a voltmeter on the battery that would help diagnose. Anything over 14.5 volts at fast idle is bad. If voltage is high, could be the regulator, could be a wiring issue, could be the alternator itself and could be something as simple as a bad ground at the regulator.

 

I repaired the damaged wires and replaced the voltage regulator, everything appears to be back to normal. I still think it's pretty odd that a symptom of a failing voltage reg was melted wires. Thanks all for the help.