225 V6 Motorola To 1 Wire Conversion

Non protected high current can produce high heat.

 

The ammeter is a d'Arsonval meter, that measures voltage just like a voltmeter. Instead of measuring the current directly, it measures the voltage drop across a low-resistance connection called a shunt. This is Ohm's law. All the charging current for the car goes through the shunt, and the more current, the higher the voltage drop and the more the meter reads.

I believe the problem comes when the shunt connections deteriorate and raise the resistance of the shunt. When the resistance increases, the voltage drop across the shunt increases, which limits the charging current to the battery. The alternator responds by increasing output to equalize the voltage between the battery terminal and the battery. The more current that goes through the shunt, the more heat is dissipated by the shunt. As the temperature of the shunt increases, its resistance increases, creating more heat. This is a positive feedback loop, and I expect it's why the ammeters self-destruct at some point.

The main problem is that all the charging current must go up to the dash, through the meter and back to the battery in an ammeter circuit. This, combined with the voltage feedback in the alternator, is what creates the opportunity for a runaway circuit if something goes wrong with the wiring.

 

What Daryl said, both times, volt meters and three wire alternators. Win Win!

 

Ammeters have been burning up cars since the advent of the alternator. More current flowing equals much more heat. Combine that with old cotton wrapped wire and you get a big ole car-b-que.

 

Just my $.02 I put a #8 wire from the alternator ground on the back of the alternator to the battery ground on the block, just to make sure that all is grounded. I have a 100 amp, amp meter off a GM diesel on my garage motor, and the GM one wire I have pegs it after starting for a few seconds.