volt meter

[Wizo]

Howdy folks; I'm getting ready to install my American auto wire, wiring harness. In the instructions It says that this wiring harness is not designed for an ammeter And that I should use a voltage meter instead. Can you guys give me your ideas or suggestions for a volt meter that will fit in the factory instrument cluster. Something that looks like it was meant to be there all along. Thanks in advance.

[leftybass209]

http://67-72chevytrucks.com/vboard/s...d.php?t=630289 start here.

[oldchevynut]

I recall a conversation I had a while back with an AAW representative on this subject and the issue is not a voltmeter/ammeter/which one gives you better information on your charging system , but rather it is a safety issue. IIRC these original ammeters at thier present age are experiencing a high failure rate of the resistor, resulting in an excessive current draw in the circuit, resulting in a significant fire hazard, so for the sake of safety and protecting your investment it is highly recommended to convert to a voltmeter, which does not have this issue. I believe he also stated that although not cheap, there are companies that will convert your original ammeter to a voltmeter. I don't have any contact information on that, but I'm sure AAW could steer you in the right direction. Randy.

[leftybass209]

No problem Wizo. If you need any advice on the conversion shoot me a message. It's beyond simple and works like a charm.

[franken]

Originally Posted by oldchevynut

I recall a conversation I had a while back with an AAW representative on this subject and the issue is not a voltmeter/ammeter/which one gives you better information on your charging system , but rather it is a safety issue. IIRC these original ammeters at thier present age are experiencing a high failure rate of the resistor, resulting in an excessive current draw in the circuit, resulting in a significant fire hazard, so for the sake of safety and protecting your investment it is highly recommended to convert to a voltmeter, which does not have this issue. I believe he also stated that although not cheap, there are companies that will convert your original ammeter to a voltmeter. I don't have any contact information on that, but I'm sure AAW could steer you in the right direction. Randy.

I think the AAW rep was confused. The battery gauge on these trucks never carried any current and there are 4A fuses in the harness to make sure no excessive current flows.

The resistor is made of wire about as thick as 3 hairs so there's no danger there.

Old Chrysler products ran current through an Ammeter and they would get hot.

[ray_mcavoy]

Originally Posted by oldchevynut

I recall a conversation I had a while back with an AAW representative on this subject and the issue is not a voltmeter/ammeter/which one gives you better information on your charging system , but rather it is a safety issue. IIRC these original ammeters at thier present age are experiencing a high failure rate of the resistor, resulting in an excessive current draw in the circuit, resulting in a significant fire hazard ...

What the AAW rep told you is true for many ammeters ... they are a fire hazard if either of the wires shorts to ground or too much current flows through the circuit. However, 67-75 GM trucks are an exception because the original wiring has two 4 Amp fuses that protect the ammeter and each of it's wires from short circuits and excessive current. Reproduction harnesses like AAW's Factory Fit line include these fuses as well.

EDIT ... looks like franken beat me to it

One of the biggest reasons why the AAW line of Classic Update harnesses doesn't support ammeters is because of the way they have configured the charging system to be compatible with modern high output alternators.

The OE ammeters in these GM trucks make use of the stock charging system's 12 gauge red wire as a "shunt". The vast majority of current flows through the 12ga wire while only a small fraction goes through the ammeter itself. That works fine with the stock charging system. But the ammeter's sensitivity is reduced when a heavier gauge wire is used to handle higher currents.

[clemsonteg]

Where are these two fuses protecting the system?

[ray_mcavoy]

Originally Posted by clemsonteg

Where are these two fuses protecting the system?

On 67-72, one of the fuses is near the battery ... not far from the junction block on the fender. The other one is over on the driver side near the voltage regulator.

The original fuse holders look like this:

[jamyers]

I'm on the lookout for a newer OEM voltmeter, but in the meanwhile I put in a cheap equus voltmeter, details are in my build thread in this post:

http://67-72chevytrucks.com/vboard/s...9&postcount=27

Hope this helps!

[Wizo]

Thanks lefty;you da man!

[BLT gmc]

Subscribed, Bruce

[clemsonteg]

Just wanted to say thanks for this thread. I realized after reading it that I only have 1 fuse for the ammeter, no fusible link, and no junction block. Ordering the parts I need to make it right

[Steeveedee]

Chrizzler used a direct current ammeter in their cars (ALL charging current ran through it! back in the day '(60s, maybe '70s?), but GM used a shunt configuration. Chrizzler had all kinds of problems with it, like thermal cycling causing the nuts on the wires at the ammeter to loosen up. A fire can be caused by the increased resistance. Also, the charging system would fail if the ammeter connections were loose. Chrizzler engineering was pretty good (Yeah, I know, go look at a '62 Dart for style, for example), but not every design works out over the years. I've worked on those systems back in the day, and have seen scorched connections.

[1968aj]

you would think if aaw told you to use a volt meter with their set they would add one to the kit. not knocking them . im about to order one myself.

[ray_mcavoy]

Originally Posted by 1968aj

you would think if aaw told you to use a volt meter with their set they would add one to the kit. not knocking them.

They probably don't include one because their Classic Update series harnesses are designed to work with a wide variety of instrument clusters ... not just stock. On the other hand, the AAW Factory Fit line of harnesses is designed to be a direct replacement for the stock wiring and they do work with the stock ammeter.

AAW does offer a voltmeter for 68-69 Camaros & 68-74 Novas that takes the place of the stock ammeter in the console gauge cluster. I don't know if they have one in the works for 67-72 trucks, but it looks like TBONE beat them to it

The voltmeter conversion he is offering should also come in handy for folks doing gauge cluster swaps into trucks originally wired for warning lights. Since the voltmeter can be hooked to the temperature gauge's existing power/ground connections, that eliminates the need to run the extra ammeter wires out into the engine compartment.

[TBONE1964]

Originally Posted by ray_mcavoy

They probably don't include one because their Classic Update series harnesses are designed to work with a wide variety of instrument clusters ... not just stock. On the other hand, the AAW Factory Fit line of harnesses is designed to be a direct replacement for the stock wiring and they do work with the stock ammeter.

AAW does offer a voltmeter for 68-69 Camaros & 68-74 Novas that takes the place of the stock ammeter in the console gauge cluster. I don't know if they have one in the works for 67-72 trucks, but it looks like TBONE beat them to it

The voltmeter conversion he is offering should also come in handy for folks doing gauge cluster swaps into trucks originally wired for warning lights. Since the voltmeter can be hooked to the temperature gauge's existing power/ground connections, that eliminates the need to run the extra ammeter wires out into the engine compartment.

Thanks Ray,

You make good valid points and for those who have changed from a non gauge (warning light) cluster to a full gauge cluster, it does take some wiring changes and the amp meter is probably the most difficult to do correctly.

Take care,
Tom

[MAC71]

This volt meter was from a 1987 truck and was $5 from a junk yard and took 10 min to install.