American Autowire Voltmeter

[pjmoreland]

I installed an American Autowire 510871 voltmeter in place of my stock ammeter. Mechanically, it fit well. The lines and text printed on the gauge are bright white instead of the light green color the stock gauges had originally. My other gauges are sun-bleached now, so they match pretty well.

The kit comes with wires and a fuse for connecting it without the use of the stock harness. The instructions say to cut off the wires that go to the original gauge at the back of the gauge cluster. Instead, I used the original wiring with the following modifications:

***EDIT***
The following approach will work, but an easier approach is shown in the diagrams in post #7
*********

1) Ground - The post on the passenger side of the gauge is the negative terminal. I used the original ammeter wire that runs to the positive distribution block by the battery for ground. I disconnected it from the distribution block and instead mounted it under the head of the distribution block mounting screw along with a star washer. This connected it to the metal of the fender. In stock form, this wire is connected to the other post of the ammeter though, so I had to swap the two engine compartment wires where they go into the bulkhead connector. The wire that runs to the junction by the alternator isn't actually needed anymore, but I left it in place. I did remove the 4A fuse from that wire though up in the front driver side corner of the engine compartment.

2) Positive Voltage - Since both wires are connected to positive for the stock ammeter, I disconnected the black wire coming from the driver side post of the gauge at the firewall bulkhead connector behind the fuse panel. I put a connector housing on this wire, and then plugged it into the Radio terminal on the fuse panel.

[pjmoreland]

More photos

[Casper42]

this is awesome! BTW how's the light transmission at nite with the dash lights - does it still look factory?
I cannot decipher your instructions however. It seems to sound easy enough but maybe I'd leave it to mechanic

[pjmoreland]

That's a good question. I haven't seen it at night yet. I'll take a look.

Let me see if I can make a decipherable schematic.

[pjmoreland]

Here it is at night. Looks the same as the other gauges

[Casper42]

Originally Posted by pjmoreland

Here it is at night. Looks the same as the other gauges

very nice! thanks for the pic!

[pjmoreland]

Here's a diagram that shows how to do this. I changed it slightly from the way I did it. The method shown on the diagram is easier than what I did because you don't have to swap terminals on the engine side of the bulkhead connector. Those terminals are sealed in with tar, so they are a pain.

The BLK and BLK/WHT wires referred to in steps 3 - 6 are located in the bulkhead connector behind the fuse panel inside the cab. The fuse panel has to be detached from the firewall to access these wires. Also, the engine side of the bulkhead connector has to be unplugged first to make it possible to insert a small screwdriver into the terminals to release them.

[franken]

A long story about (GM) the battery gauge (not Ammeter) measures the difference in voltage between the battery and alternator.
A Voltmeter measures Voltage between one point and another.
A long story made short.

[pjmoreland]

An ammeter measures current. The stock battery gauge displays the magnitude and direction of the current flow between the alternator and the battery. It does this by measuring the voltage drop on a known resistance, which is the resistance of the wire (shunt) that connects the alternator to the battery. While it is true that the stock gauge is on its own a voltage-driven gauge, it is in effect an ammeter when combined with the shunt that it is measuring.

[franken]

Nonsense. If you think that a gauge (labelled C, D and named battery) that has no increments and a random bit of wire (of only approximate resistance) manage to indicate anything more than the relative amount of current flow in one direction or another, you're confused.
Feel free to show the magnitude of the current on a stock gauge by any means. BTW, magnitude in this cae is measured in Amperes, which the battery gauge makes no attempt to show..

[pjmoreland]

Originally Posted by franken

Nonsense. If you think that a gauge (labelled C, D and named battery) that has no increments and a random bit of wire (of only approximate resistance) manage to indicate anything more than the relative amount of current flow in one direction or another, you're confused.
Feel free to show the magnitude of the current on a stock gauge by any means. BTW, magnitude in this cae is measured in Amperes, which the battery gauge makes no attempt to show..

The magnitude is indicated by how far from center the needle deflects. The direction of flow is indicated by whether the needle deflects to the left or to the right of center.

[Already Gone]

Originally Posted by pjmoreland

Here's a diagram that shows how to do this. I changed it slightly from the way I did it. The method shown on the diagram is easier than what I did because you don't have to swap terminals on the engine side of the bulkhead connector. Those terminals are sealed in with tar, so they are a pain.

The BLK and BLK/WHT wires referred to in steps 3 - 6 are located in the bulkhead connector behind the fuse panel inside the cab. The fuse panel has to be detached from the firewall to access these wires. Also, the engine side of the bulkhead connector has to be unplugged first to make it possible to insert a small screwdriver into the terminals to release them.

Is this the instruction page from American Autowire that comes with the gauge ?

[pjmoreland]

Originally Posted by Already Gone

Is this the instruction page from American Autowire that comes with the gauge ?

Definitely not. Their instructions say to cut the original wires and add new separate wires that run loose behind the dash down to the fuse panel.

[RustyPile]

Originally Posted by pjmoreland

Definitely not. Their instructions say to cut the original wires and add new separate wires that run loose behind the dash down to the fuse panel.

Now I understand why you did it as you did.. Is their chief electrical engineer a red neck bubba?????

[pjmoreland]

Originally Posted by RustyPile

Now I understand why you did it as you did.. Is their chief electrical engineer a red neck bubba?????

Haha. Well their instructions are at least very thorough and simple to execute and maybe less likely to set your truck on fire if you don't follow them exactly.

[RustyPile]

Originally Posted by pjmoreland

Haha. Well their instructions are at least very thorough and simple to execute and maybe less likely to set your truck on fire if you don't follow them exactly.

Dangling wires under the dash??? Less likely to start a fire??? Well, put 'em in pdf format and email 'em to me and let me decide...

[pjmoreland]

Here's a video that shows the voltmeter in action:

https://youtu.be/bI4oaCpElOU

[PbFut]

What are you attempting to monitor? To be clear the terminal you attached to is not meant for attaching accessories but is a good point for monitoring voltage at the battery and alternator output for charging. It is a not so good point if you are looking for health of the system relative to powering the ignition and accessories. The fuse block would be a better choice for the system monitor. Or a balance would be at the main splice. To be clear the 12v post on the fender next to the battery was never intended as a aux power post. It is there simply to be able to replace fuse links without damaging the harness. Pulling power for accessories from the fuse link post creates a false signal to the factory battery meter making a discharge appear to be a charge state because the draw is at the wrong end of the shunt lead that runs from main splice to the fuse link post. The battery meter works perfect if you connect accessories at the main splice and adjust the shunt lead size for balance and overloads. All my added fans draw at the main splice. I went up one size on the shunt wire. The battery meter does not pin with alternator not spinning and battery powering fans and other stuff but does correctly indicate discharge. With an aftermarket alternator, off idle will generate enough power to swing past center to a charge state while fans are running indicating I am producing more power than truck is using and battery is charging just off idle. At idle in summer with ac lights and fans running I just tip to discharge at idle. Go up just a few hundred RPM then it is s sending excess to the battery. The volt meter may or may not provide the instant information on charge state desired. But it is way easier to wire correctly assuming you are clear on what you are actually trying to monitor.

[pjmoreland]

My intention was to install a voltmeter while impacting the original wiring as little as possible. Please note that I am not using the 12V terminal block at all. I am grounding the wire that used to be connected to the terminal block (see the diagram I posted above).

[Accelo]

Come on guys.
pjmoreland just changed the wiring that feeds the gauge. Instead of at the gauge like the aftermarket vendor suggested.
It works perfect and there is so little current at the gauge it's almost not measurable.
I modified my own Volt meter wiring at the gauge. I only wish I would have thought of the solution pjmoreland did. I think it's a perfect solution that makes the wiring look stock.

I loved the excellent drawings. Great Job.
Cheers

[pjmoreland]

Thank you,, Accelo.

I should mention that while it would be nice to have the voltmeter tied to the 12V wire junction inside the harness near the alternator from an accuracy perspective, the voltmeter needs to be connected to a SWITCHED source so that it doesn't remain on and drain the battery when the truck is off.

I should also mention that I have modified my front harness with heavier gauge wires to handle a higher output alternator, and I have an EFI system and Vintage Air system both connected directly to the battery. These three changes made the stock ammeter ineffective. A voltmeter can at least tell me the health of the battery when I first turn the key to run before starting the engine. It can also tell me the health of the alternator and its internal regulator once the engine is running.

[PbFut]

Sorry, I think I am being misunderstood. I did not say the wiring was wrong. It is fine if you are looking for voltage at the battery. With these old systems it is easy to get low voltage at other points in the system. What the user is attempting to monitor is a huge driver as to where the meter is connected. It's not the meter draw that is the point. It is the device(s) drawing power and size of leads that changes things. Not criticizing op's idea, but changing a factory lead from a positive post to ground is a questionable practice, for future unsuspecting owner.

[pjmoreland]

There is a fuse on that 12V wire converted to ground wire, so I'm not concerned about that. If someone came along and decided to move that wire back to positive voltage, nothing would happen since there would be positive voltage connected to both terminals of the voltmeter. That would result in zero current flow through the voltmeter.

[pjmoreland]

My 12V connection for the voltmeter is at the fuse panel. There are really no other practical options since it has to be switched 12V with a voltmeter. The ground connection just needs to be a reliable ground.

Since you are still running the stock ammeter, it makes sense to attach your fans where you did. With a voltmeter installed, I see no issue with connecting accessories at the 12V terminal block by the battery since the only reason to avoid that is to preserve the functionality of the stock ammeter. This assumes the wire running between the battery and alternator is big enough to handle the load of the entire system. The EFI and A/C systems I installed had explicit instructions to connect their power leads directly to the battery, which doesn't work well with the stock ammeter.

[54blackhornet]

On a 71 model year can you tell me where on the fuse panel you would hook up a voltmeter? I have my HEI hooked to the listed as fused…thanks