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George;
I usually agree with your good information, its based on experience, sound engineering practices and principles...but this time without recognizing the advantage of an Ampmeter, you have simply condemned it...the discussion for/against Amp/Voltmeters is not that straightforward, and the points which you have stated as disadvantages against Ampmeters are not valid IMO, and I dissagree with what you state is an advantage of the Voltmeter...
1. "ALL the current has to pass through the ammeter to give valid readings.
Bad wiring = FIRE." Yes an Ampmeter must be connected with heavy gauge wire, but wire doesn't generally "go bad" by itself...wires typically fail and get hot if they are overburdened or allowed to vibrate or abrade on sharp corners which compromises the insulation (=improper installation), so using 600V insulation (double thickness compared to the standard 300V) AND sleaving on AMPmeter wiring which runs through the firewall is definately in order (in any car wiring!)...there is an additional risk in that there is now a wire essentially connected to the bat (and therefore capable of high currents) running behind the dashboard, but so what, there plenty more of those! Replacement bat. cables also have a "fusible link" which limits current which can be passed through this cable...and the AMPmeter makes a good place to connect addition loads in a vintage Volvo so as not to put additional current through the original wiring. Finally, I would say that there is no more risk for having a fire in Ampmeter wiring than having a fire in any other wire...
2. "Voltmeter gives better info and can be hooked up easily about anywhere in the system." I have to dissagree with this statement also - A Voltmeter indicates the system voltage, and depending on a number of factors (like state of charge of bat., loads turned ON, temperature), this is pulled up and down quite a bit, so if the point of installing a meter in the first place is to be able to monitor the (A)health of the charging system and (B)state of charge of bat., it doesn't do either one very well...(A)state of the charging system is not easily determined (because of this variation depending on loads), and (B)neither is the state of charge of the bat (from 10% charge to 90% charge occurs within 0.75V!, temp dependent)...I fail to see where this can be considered to be "better info". It does have the advantage of being able to be connected with a small gauge wire.
Ampmeter on the other hand, is split into two areas, charge and discharge...interpreting its indication is much simpler...if the indication is ever in the discharge area while engine is running, charging system is not putting out adequitely to keep up with loads...not much interpretation necessary...
More here: http://www.sw-em.com/elecramb.htm
The bottom line is that either one is head and shoulders above an "idiot light" only.
Cheers
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