by Austin Jack Smith
Basically, there are two types of ampere meters, one uses an internal "shunt" to read the flow of electricity, which means all power going from, or too your battery must pass thru the meter which requires another pair of wires from the end of the bus to the front. This wiring type is called "wired in series" This additional wiring will result in a drop in voltage to your systems, this drop is called "line loss" and will be noticable so I think this would render a internal ampere meter a very poor choice.
Another type of ampere meter, which would be very expensive, is a type that requires a small "shunt" to be placed next to the battery, instead of inside the meter, which results in a very small line loss because the total electrical passes thru the shunt and a very small pair of wires goes to the ampere meter which is then reads this flow as total amperage flow, although it is just a small amount, cost wise this would eleminate this type of ampmeter. Unless you just had to have this information.
To provide a really good source of electrical information is a Voltmeter, which are very popular in the newer cars. Because it does tell you the status of your electrical system. Low voltage when you switch on prior to engine rotation tells you your battery is getting old and not holding a charge or you left something on and ran your battery down. While an increase in battery voltage after engine start will tell you your electrical generating system is working and the voltage remaining a steady reading of say 14.3 Volts indicates that your voltage regulator is functioning properly, this should remain steady regardless of the "load" placed on the system, of course when the engine is idling, you shouldn't expect to run all the equipment at once.
The biggest plus of a voltmeter is that it is in parallel with your
system and only requires a very very small amount of power to run it.
The power can be taken from any convient source that is on when the
ignition is switched on. It is also much cheaper to buy as well.