Amp gauge issue

[DoubleE]

Newbie to the site. Have recently sold my 62 SS and purchased a 72 C10 short box. My new ride has the full gauge instrument cluster which I suspect one of the previous user's installed. Everything works but the amp (battery) gauge. I have read some older posts here on the subject and understand the basic operation as it's applied to the C10. One thing not mentioned is if the wiring harness along with the gauge cluster needed to be swapped out for this to work.

I was very surprised to see the differences in the pin-out between the idiot light vs the full gauge clusters. I have not torn into this yet but wanted to do some research ahead of time.

Reading thru the old posts seems like they were side tracked on what is a volt mete vs an amp meter is. A couple of poster's were on the right track but should have made the point that ALL electrical meters are based on the D'Arsonval meter movement. Both the Amp meter and Voltmeter are D'Arsonval meter movements that are modified for their specific application using shunt circuits and how they are connected to the circuit configuration being measured.

Eric

[davepl]

Have you checked the two small fuses in the front corners of the underhood wiring harness? Both fuses need to be present (and good) for the ammeter to work properly. My replacement harness was missing them for some reason (holders were there, but empty).

If he went to the trouble of changing the cluster, he likely changed the PCB too, and other than that I don't know if/what specific differences there are in dash harness between a gauge and light cluster.

In keeping with the old "When you see hoofprints, think horses, not zebras", I'd find and check the fuses (horse prints) before suspecting the wrong wiring harness (zebra prints).

[LockDoc]

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First off welcome to the board.

I can tell you already know a lot more about this stuff than I do. I do know that you won't see much movement in the truck gauge needle. Out of all of the trucks I have had only a couple of them had a gauge that you could actually see the needle move. There are two 4 amp fuses in the circuit that have to be in good condition before the gauge will work. There is one on each side of the core support in small black rubber holders. They are notorious for breakage and corrosion. I would check those first.

LockDoc

[davepl]

FWIW mine will peg the gauge with a 100A alternator ('84 Camaro, I think, same CSI case but better guts). With the stock 36A or 42A Delcotronarator I doubt it does move much to the Charge side, but you can still see Discharge pretty easy with the high beams on and the truck not running.

OP sounds like he's up to speed, but these are a shunted voltage differential gauge, not really an ammeter. An actual ammeter would measure flow between the battery and the truck, and would need an inline connection. This one taps at the alternator and I think the reference voltage is the PCB itself, and then it compares and moves the needle. Be easier in software :-)

[LockDoc]

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It is my understanding that the stock gauges don't show the amount of current flowing, just which direction it is going.

LockDoc

[davepl]

Originally Posted by LockDoc

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It is my understanding that the stock gauges don't show the amount of current flowing, just which direction it is going.

LockDoc

You can likely establish this yourself by turning on the headlights, then the high beams, then the fan on Hi, and see if it moves more each time.

I can't verify the trucks, but in the 1969 Bonneville the gauge package does indeed show the amount of current (measured roughly how I describe it).

I used to have the factory alternator, it'd move about 1/4". With double the power, it moves about 1/2". No idea if it's really linear, but it certainly did charge a lot "more" once I upgraded the alternator.

[leftybass209]

Welcome!!!!!! The wiring is all wrapped as one harness. If you can live with rewrapping it, then it's easy to add the wires. The terminals on the firewall harness aren't being used by anything. You can find great color schematics of the entire harness on the forum.

Are you set on using the amp gauge, or have you considered modifying it (assuming you want to keep the OEM design) to become a voltage gauge? If so, there's some good tech threads here how to utilize a square body gauge to convert the OEM amp one, and would eliminate the need to run extra wiring for the amp gauge.

Best of luck with your new toy!

[Andy4639]

Hello and welcome to the board.
I've been driving my 71 now for almost 30 years. I swapped the amp gauge out for a good volt gauge and never looked back.
The amp gauges in these trucks will only move enough to say it may have moved if you where looking at it when you turned something on. Most of the time it's a flicker at best.
Here is a link to the wiring schematics.


http://67-72chevytrucks.com/vboard/s...d.php?t=185856

[VetteVet]

Originally Posted by DoubleE

Newbie to the site. Have recently sold my 62 SS and purchased a 72 C10 short box. My new ride has the full gauge instrument cluster which I suspect one of the previous user's installed. Everything works but the amp (battery) gauge. I have read some older posts here on the subject and understand the basic operation as it's applied to the C10. One thing not mentioned is if the wiring harness along with the gauge cluster needed to be swapped out for this to work.

I was very surprised to see the differences in the pin-out between the idiot light vs the full gauge clusters. I have not torn into this yet but wanted to do some research ahead of time.




Reading thru the old posts seems like they were side tracked on what is a volt mete vs an amp meter is. A couple of poster's were on the right track but should have made the point that ALL electrical meters are based on the D'Arsonval meter movement. Both the Amp meter and Voltmeter are D'Arsonval meter movements that are modified for their specific application using shunt circuits and how they are connected to the circuit configuration being measured.

Eric

D’Arsonval meter movement and its principle




D’Arsonval movement principle :

An action caused by electromagnetic deflection, using a coil of wire and a magnetized field. When current passes through the coil, a needle is deflected.

Whenever electrons flow through a conductor, a magnetic field proportional to the current is created. This effect is useful for measuring current and is employed in many practical meters.
Since most of the meters in use have D’Arsonval movements, which operate because of the magnetic effect, only this type will be discussed in detail. The basic dc meter movement is known as the D’Arsonval meter movement because it was first employed by the French scientist, D’Arsonval, in making electrical measurement.





This type of meter movement is a current measuring device which is used in the ammeter, voltmeter, and ohmmeter. Basically, both the ammeter and the voltmeter are current measuring instruments, the principal difference being the method in which they are connected in a circuit. While an ohmmeter is also basically a current measuring instrument, it differs from the ammeter and voltmeter in that it provides its own source of power and contains other auxiliary circuits.

D’Arsonval Galvanometer :

This instrument is very commonly used in various methods of resistance measurement and also in d.c. potentiometer work.

Construction of D’Arsonval galvanometer:

D'Arsonval Galvanometer

1) Moving coil:

It is the current carrying element. It is either rectangular or circular in shape and consists of number of turns of fine wire. This coil is suspended so that it is free to turn about its vertical axis of symmetry. It is arranged in a uniform, radial, horizontal magnetic field in the air gap between pole pieces of a permanent magnet and iron core. The iron core is spherical in shape if the coil is circular but is cylindrical if the coil is rectangular. The iron core is used to provide a flux path of low reluctance and therefore to provide strong magnetic field for the coil to move in. this increases the deflecting torque and hence the sensitivity of the galvanometer. The length of air gap is about 1.5mm. In some galvanometers the iron core is omitted resulting in of decreased value of flux density and the coil is made narrower to decrease the air gap. Such a galvanometer is less sensitive, but its moment of inertia is smaller on account of its reduced radius and consequently a short periodic time.

2) Damping:

There is a damping torque present owing to production of eddy currents in the metal former on which the coil is mounted. Damping is also obtained by connecting a low resistance across the galvanometer terminals. Damping torque depends upon the resistance and we can obtain critical damping by adjusting the value of resistance.

3) Suspension:

The coil is supported by a flat ribbon suspension which also carries current to the coil. The other current connection in a sensitive galvanometer is a coiled wire. This is called the lower suspension and has a negligible torque effect. This type of galvanometer must be leveled carefully so that the coil hangs straight and centrally without rubbing the poles or the soft iron cylinder. Some portable galvanometers which do not require exact leveling have ” taut suspensions” consisting of straight flat strips kept under tension for at the both top and at the bottom.

The upper suspension consists of gold or copper wire of nearly 0.012-5 or 0.02-5 mm diameter rolled into the form of a ribbon. This is not very strong mechanically; so that the galvanometers must he handled carefully without jerks. Sensitive galvanometers are provided with coil clamps to the strain from suspension, while the galvanometer is being moved.

4) Indication:

The suspension carries a small mirror upon which a beam of light is cast. The beam of light is reflected on a scale upon which the deflection is measured. This scale is usually about 1 meter away from the instrument, although ½ meter may be used for greater compactness.

5) Zero setting:

A torsion head is provided for adjusting the position of the coil and also for zero setting.

Happy Now:

[Andy4639]

And to think all this time you never had a funny side vet!

[Carmen Black]

I will readily admit I that I don't understand anything about ammeters. However, when I did the American Autowire Classic Update kit to completely rewire my truck, the kit did not have a connection to the ammeter.

If I remember correctly, American Autowire does this on purpose due to the fact that if you are running a more modern / powerful alternator, it could cause the ammeter to overheat and catch fire.

I would just check to make sure it has the old stock alternator and still has the old external regulator.

[DoubleE]

Tnanks to all who replied. Today is Thanksgiving Day, 1st chance I have had to get back to the forum.
So I have a couple more questions concerning the wire harness. I'm 99% sure the under the dash harness is different depending if used with the idiot light or gauge cluster due the differences on the pin-out of the 2 clusters. It's my guess that the PO must have switched out this harness too or none of the other gauges (fuel) would be working (they do). With that said my next question is the engine/light harnesses - would they be different too? Haven't had a chance to look for the 2 fuses mentioned. If they are not there its my guess they did use different harnesses. If they are there then maybe they used the same harness for both applications.

The other thing I failed to mention is that the previous owner kept all his receipts and gave them with the truck. One was for the gauge cluster from a salvage yard - no mention of a wire harness though.

Interesting comments about the sensitivity of the gauge (or lack there of). I had never seen any deflection in the needle so did the headlight test with NO movement which led me to conclude it's not connected.

Hopefully I will get the chance to stick my head under the hood today!

Eric

[VetteVet]

............

Originally Posted by DoubleE

Tnanks to all who replied. Today is Thanksgiving Day, 1st chance I have had to get back to the forum.
So I have a couple more questions concerning the wire harness. I'm 99% sure the under the dash harness is different depending if used with the idiot light or gauge cluster due the differences on the pin-out of the 2 clusters. It's my guess that the PO must have switched out this harness too or none of the other gauges (fuel) would be working (they do). With that said my next question is the engine/light harnesses - would they be different too? Haven't had a chance to look for the 2 fuses mentioned. If they are not there its my guess they did use different harnesses. If they are there then maybe they used the same harness for both applications.

The other thing I failed to mention is that the previous owner kept all his receipts and gave them with the truck. One was for the gauge cluster from a salvage yard - no mention of a wire harness though.

There are minor differences in the harnesses but this conversion has been done hundreds of times without changing the whole harness.
You will have to change the pins on the cluster plug and remove a couple of wires and add the two black wires for the ammeter.

Here is a thread that should answer most of your questions.

http://67-72chevytrucks.com/vboard/s...p?t=295681ions.



Interesting comments about the sensitivity of the gauge (or lack there of). I had never seen any deflection in the needle so did the headlight test with NO movement which led me to conclude it's not connected.

Your gauge probably isn't working especially if you haven't rewired the cluster.

Hopefully I will get the chance to stick my head under the hood today!

Eric

[Lattimer]

Originally Posted by DoubleE

Tnanks to all who replied. Today is Thanksgiving Day, 1st chance I have had to get back to the forum.
So I have a couple more questions concerning the wire harness. I'm 99% sure the under the dash harness is different depending if used with the idiot light or gauge cluster due the differences on the pin-out of the 2 clusters. It's my guess that the PO must have switched out this harness too or none of the other gauges (fuel) would be working (they do). With that said my next question is the engine/light harnesses - would they be different too? Haven't had a chance to look for the 2 fuses mentioned. If they are not there its my guess they did use different harnesses. If they are there then maybe they used the same harness for both applications.

The other thing I failed to mention is that the previous owner kept all his receipts and gave them with the truck. One was for the gauge cluster from a salvage yard - no mention of a wire harness though.

Interesting comments about the sensitivity of the gauge (or lack there of). I had never seen any deflection in the needle so did the headlight test with NO movement which led me to conclude it's not connected.

Hopefully I will get the chance to stick my head under the hood today!

Eric

I have done the idiot light to gauge swap on my truck. There is a very good set of instructions on GMC Paul's site about halfway down this page:
http://www.gmcpaulstruckparts.com/Tech%2520Tips1.htm

Note that you need to add a wire to make the amp gauge work.

So, step one, take a look to see if that wire was added. If not, you need to add one. If it is there , it should be fused, so check the fuses. The other things o check would be that the gauge is grounded. I had trouble with the ground on the restored cluster I bought and had to add grounds to make everything work.





I run a 120 amp internally regulated alternator, and the gauge works ok. It never goes negative, but it does show the increased output of the alternator when the lights or fans are on, etc.

I also have a voltmeter, so the amp gauge is not all that useful, but I wanted it operation for the sake of completeness.

[VetteVet]

...........

Originally Posted by Carmen Black

I will readily admit I that I don't understand anything about ammeters. However, when I did the American Autowire Classic Update kit to completely rewire my truck, the kit did not have a connection to the ammeter.

If I remember correctly, American Autowire does this on purpose due to the fact that if you are running a more modern / powerful alternator, it could cause the ammeter to overheat and catch fire.
I would just check to make sure it has the old stock alternator and still has the old external regulator.

They are most likely referring to the older style ammeters that had all the alternator output run through them. They were limited to 60 amps IIRC. The 64 and newer ammeters are wired in parallel with the alternator and only a few milliamps goes through the meter. It also has two four amp fuses inline with the wires so they protect the meter.

We have lots of members running the newer SI style and the CS 100 amp alternators with the stock battery gauge with no problems. They will work just fine provided they are wired correctly, even with a one-wire alternator.