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Discussion Starter #1
I just installed aftermarket amp gauge in line with horn relay wire from battery on 68 with voltage reg.
the amp gauge reads zero and goes negative slightly with lights on or when start car.
but does not register positive for charge.
dummy light in dash for gen goes on when key turned and goes out when car starts.
is car charging? or is amp gauge hooked up wrong??
I have not yet checked volts of system when running.
does volt reg need adjusting?>
 

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All amp guages are really millivolt meters connected across a low value resistance known as a shunt. (There are internally shunted meters, but not on Camaros to my knowledge).

The low value shunt in your car's electrical system is the wire connecting the horn relay to the juntcion block behind the battery on the radiator support. So the amp meter should be connected to both the horn relay and to the junction block.

Since the relay/B+ wire is your shunt, changing it's size will alter the meter's calibration. If you upsized the wire, as many folks do with an internal regulator conversion, the meter will read lower than normal. You may be able to compensate for the problem by changing a resistor on the back of the guage - I don't know for certain. If the guage does not have a resistor calibrator accross it's terminals you might be able to install a few ohms of resistance in series with the amp meter leads to offset it. But usually it isn't necessary. The gauge is really just a visual indicator of charge / discharge. Probably the factory setup was calibrated to no better than +/- 10% of Full Scale.

Since the meter is a millivolt meter, if you connect one terminal to B+ and the other to ground, you'll likely damage the meter movement. 12 volts is about 240 times overscale for a typical ampmeter (millivolt meter). Looks like I duped Mark C.'s point. BTW, the +/- 0.5 volt claim is probably correct. I personally haven't measured it.

To confirm the hookup, use a digital volt meter. You should be able to read just a few millivolts on the amp meter's terminals as loads are varied on the electrical system.

If you know the resitance of your shunt (by measuring it out of circuit). You can translate the voltage drop across the shunt with the current through it. Ohms law says:

I = E / R

'I' is the current through the circuit. 'E' is the voltage or eltromotive force measure accross the resistance 'R'. So if your horn relay / junction block line has a resistance of 0.1 ohm, and you measure 0.100 volts across the line, the current load is 0.1 Ohm / 0.100 volt = 1 Amp.
 

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Discussion Starter #4
Mark,
Thanks for reply
It is an aftermarket amp gauge, not original camaro gauge.
I followed instructions, just like your second link, disconnect 10g red going from battery to horn rely, attached wire to amp gauge ,other gauge post to horn rely where wire came from.
I think it is working, as reads small amount of neg amps when lights are on or starting, but does not read positive as if it were charging.
But the dummy light appears to work, indicating my alternator is working.
how can this be?
 

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Discussion Starter #5
dnut,
I used electrical wire from home depot
10 g copper strand, not solid.
does home wiring have more resistance than auto wire? different size wire strands?
 

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What's the scale of the meter? It only reads slightly positive or negative because it's only measuring the current go to or coming from the battery, not whats coming out of the alternator. The alternator supplies all the current necessary to operate the car, and if there is any left over it charges the battery, if the battery needs it. The battery may need 5 or 10 amps for the few minutes after a start, and it may put out a few amps as soon as you turn the lights on, until the voltage regulator can increase the voltage to the alternator field which will increas the alternator output to make up for the current drawn by the lights. So if you have a 60 or 100 amp ammeter I wouldn't be shocked to see the needle barely move in either direction. You need to get the meter inline with the red wire from the alternator in order to see anykind of needle deflection on the gauge.

Of course running 30, or 50 or 100 amps thru an ammeter, inside your car is just asking for a fire someday. Theres a reason all the car manufacturers use millivolt meters instead of direct reading ammeters in their cars. Direct reading ammeters are not safe.
 

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Your home depot wire should work just fine. For DC circuits, solid wire is usually used. But car wiring is different. Vibration is a killer thus the use of stranded wire. Also, stranded wire will bend an lay down easier than solid wire.

But since you up sized the wire, it will be capable of carrying more current due to it's lower resistance. So for a given current applied, there is less voltage drop generated across the wire. That is why the gauge will read less than normal.

There is no difference between automotive wire and other wire from a current carrying perspective. The only difference you'll find is that automotive wire tends to be made from smaller strands to make it more flexible. Also, the insulation may be better suited for heat and exposure to oils etc. What you have will probably work just fine.
 

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Discussion Starter #8
thanks for all the help guys
I did put it in line with the alternator and it works now.
I guess someone changed the wire from the horn relay to battery at one time, though it does have a seperate working volt reg now and old type alternator.

I assume my amp gauge is only measuring alt output and will not show a problem with a bad volt reg or battery installed here.
better than nothing.

But I am now concerned with the high amps and fire potential.
Would it help to install inline fuses on the 2 10g new wires to and from the amp gauge?
A fire would be caused by shorting to ground and a fuse would isolate this, probably best placed at alternator to protect circuit running through car. 40 amp fuses? I am not sure what amp the alt is- Should it be labled?

Or maybe I'll entertain installing a volt gauge instead-I always thought amp gauges were better indicators.
 

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Alternators are labeled on the top just behind where it bolts to the upper support bracket. Stock alternators, are 37A, 61A, or 62A.

If you have a problem with the either the battery or the voltage regulator then you will have a problem with the alternator, it will either stop putting out current (usually), or put out more than it's rated for. The output of the alternator is the only place you can put an in line ammeter, just make sure you have the connections located between the alternator output terminal and the first splice in that main wire (which is before the wire gets to the horn relay). The splice is where the main power is split between the fuse panel and the horn relay, which in turn feeds the battery. If your connected below the splice it will not indicate the full alternator output current on the gauge.

Put a fuse in line with both legs of the ammeter just larger than the alternator output. Alternately, you could put in a few inches of #14 gauge wire on each leg, to act as a fuseable link.
 

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Discussion Starter #10
I just unconnected wire from back of alternator and put in line my new wires so power is routing from alternator, through my gauge in car and back to original wire going throughout car-I assume first point to horn relay??
Is this OK?
This new wire, about 12ft 10g, wont drag down charging of system, will it, being right after alternator?
 

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Yes that will show you the alternators true output. Length of alternator output wire doesn't affect alternator output, it's controlled by battery (or system) voltage, the voltage regulator will increase the field strength in the windings of the alternator until the desired voltage level is reached at the battery (actually measured at the horn relay terminal).
 

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Discussion Starter #12
It all sounds good.
Thanks for all the assistance Mark and dnult.
without your help, I would have been messing with my alternator and regulator, removing and checking for fault.
Instead, I'm up and running.
 

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If you connect it to the alternator output you will only show charge or nothing. When it is installed between the relay and the junction block you'll get a true indication of charge and discharge of the entire system.

Instead of a fuse on the big wire, consider a fusable link. It will prevent a complete meltdown, but won't create the resistance that a fuse will.
 

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Discussion Starter #14
Thanks Dave,
It is working and does show what alternator is doing.
I tried connecting originally at horn relay post and that is when I got nothing, I guess from an upsized wire to battery, so this wont work.

Could I try connecting at same wire, but at junction stud infront of battery instead?
Will this give better readings?
I will use the fusible link, a 14 ga wire, about 2" Long?
thanks
Rick
 

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Yes, there should be 2 wires for the amp meter. (Disconnect the battery before messing with it, or else you're amp meter will blow if it gets 12volts across it). One terminal should connect to the juntion block by the battery, the other should connect to the horn relay. This way it will show both charge and disharge as it should. The alternator can only charge. It has diodes in it that prevents current from running the other way.
 

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Won't work that way. He has an aftermarket real current reading Ammeter, not the millivolt meter stock GM ammeter. I'm assuming its a plus or minus 40 or 50 amp gauge (never did get the scale info). He has to put the output of the alternator thru the meter to make it read. There is not enough current flowing into or out of the battery to make the gauge deflect and there is no way to wire the car up to show a current discharge should the alternator die.

A current reading ammeter is used to read the output of the alternator (or the battery), the stock millivolt meter is used to determine if the battery is being charged or discharged. If the gauge had a lower range, like -10 to +10 amps you could wire it up like the stock gauge and get the needle to move enough to tell which way current was going.
 

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So Mark, are you saying the meter scale only has positive values on it instead of postitive and negative values? So the meter has 10 guage wire going to and from the amp meter?
 

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No, I'm saying that on an ammeter with a 50-0-50 scale (or something like that) there isn't enought current going to and from the battery under normal conditions to move the needle in either the charge of discharge direction. Most of the alternator output goes straight into the fuse box to run lights, radio, fan etc. Very little current goes to the battery except right after engine start.

Of course the meter will operate if it's wired like the stock gauge, it just won't show much needle deflection one way or the other. A smaller scale "real" ammeter would be better suited to be wired into the red wire running from the horne relay to the battery. Something with a scale on the order of 10-0-10 amps, or 20-0-20 amps. At least then the needle will move off the 0.

The only place that you can get the kind of current that will cause the needle to move is directly from the alternator. Of course placing it there will only cause the gauge to read in the positive direction. Unfortunately there is no place to wire that into a camaro which will show both charge and discharge, because the scale of the meter is to large.
 

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what is the point of an ammeter? a volt meter tells you whether the alt is working or not- if it reads over 12 volts when running, it is working. if it reads lower than 12 volts when running, it isn't charging.
plus, a volt meter is so much easier to wire up and much safer.
 
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