Battery/amp gauge

[72lb4x4]

Originally Posted by VetteVet

Here's the definition of an external shunt ammeter which is what we have in our trucks.

An external shunt is basically a very low value resistor that is in series just as the ammeter was in the previous example, and then the ammeter is in parallel to the shunt. Basically MOST of the current goes through the shunt and only a small percentage goes through the ammeter. By knowing the resistance of the shunt and the meter, the meter is able to calculate the total current by measuring only the small current that goes through the meter. This kind of setup allows small wires to be run to the ammeter in the cockpit, and the high current to remain in the engine compartment. The danger in these setups on some old cars is there isn't a fuse on that small ammeter wire, So if the shunt is damaged or a connector breaks, it would try to flow all the current through the remaining path which is the small ammeter wire and that would melt that wire (along with whatever else it is next to).

This is the reason there are 2 small fuses in the wiring circuit on our trucks that have battery gauges. They are actually amp meters since they measure amperage differential and not volt meters because there is no connection to the negative side of the circuit.

Sorry, but you just don't understand what you're talking about. Your last sentence, among others, proves this.

The meter that reads in amps in a shunt ammeter is still a voltmeter measuring the voltage across the shunt resistor.

Look at the battery gauge and you'll see that it will fry before anything else in the circuit.

You might want to try using a web search to learn what an actual ammeter is and how it works.

The OP may want to look into the differences in the two underhood harnesses to see if they are missing the wires needed to make the gauge work.
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