Amp vs volts

[mtchevytruck]

Another question for the masses. Found a factory tach cluster out of a 73' with an amp gauge. Plan on installing it in my 77' which has a volts gauge. Will either work with the three wire alt. and is one more desirable than the other if I have the choice?

[Fixwhataintbroke]

http://www.73-87.com/7387garage/inte...achometers.htm

[silvereagle07]

Originally Posted by Fixwhataintbroke

http://www.73-87.com/7387garage/inte...achometers.htm

This kinda jumped out at me from this page...

1. AMP or VOLT gauge mix-ups could cause a fire.

[mtchevytruck]

Thanks for the info! Almost started the swap today from a 72' to a 77'. Hoping to build one out of two carefully.

[mtchevytruck]

Got it done successfully! More differences in clusters than I would have thought. Volt and amp gauges are not interchangeable!! Amp gauge has, in layman's terms, full voltage running through it in a continuous stream of current. Volt gauge is more like other basic gauges with a power, ground, and a feed wire that fluctuates (more or less) either positive or negative.

[THE "10" SILVERADO]

Originally Posted by mtchevytruck

Got it done successfully! More differences in clusters than I would have thought. Volt and amp gauges are not interchangeable!! Amp gauge has, in layman's terms, full voltage running through it in a continuous stream of current. Volt gauge is more like other basic gauges with a power, ground, and a feed wire that fluctuates (more or less) either positive or negative.

Yeah I asked about that a while back since I had been wanting to see the difference.....even though that cluster had a amp couldn't you just take out the amp gauge and put in a volt gauge? But yeah, from the responses amp gauges were a bad thing if you wanted to put in a new one...

[Altec]

I wouldn't let horror stories of people who didn't know how to properly wire a ammeter, or poor factory setups from the 70's set your opinion of ammeters.

I prefer a good ammeter myself. It can tell me the same thing a voltmeter will about my battery being low, and it will give me a better idea of my charging system.

Anything is better then a idiot light though!

[mtchevytruck]

Originally Posted by Altec

I wouldn't let horror stories of people who didn't know how to properly wire a ammeter, or poor factory setups from the 70's set your opinion of ammeters.

I prefer a good ammeter myself. It can tell me the same thing a voltmeter will about my battery being low, and it will give me a better idea of my charging system.

Anything is better then a idiot light though!

Altec, I agree and was hoping on installing the amp meter instead of the volt meter, but would have had to do additional wiring in the harness and maybe a different alternator?

[72lb4x4]

Ammeters causing fires in these trucks is pretty much a myth unless an aftermarket meter is installed.

In reality the GM gauge is measuring the difference in voltage at 2 points in the wiring harness. One point near the battery and one near the alternator. If the voltage at the battery is higher, the gauge indicates discharge. Higher at the alt, it indicates charge. The difference is in tenths or thousandths of a volt.

[78 Chevyrado]

Volt meters connect to the hot wire and tell you the voltage present in a system. The volt meter is a closed loop all on its own and is built light since not much amperage runs through it at all

amp meters show you the amperage draw to the battery, which means ALL system current runs through the amp gauge. the amp gauge is inline with the main power wire. amp meters are built heavy because heavy current runs through them.

Volt meters are better IMO.

[Justins76]

Anyone know if 73+ trucks use a shunt type ammeter?

[Justins76]

Originally Posted by mtchevytruck

Another question for the masses. Found a factory tach cluster out of a 73' with an amp gauge. Plan on installing it in my 77' which has a volts gauge. Will either work with the three wire alt. and is one more desirable than the other if I have the choice?

This may be of help to you. Use your stock voltmeter and move the terminal post as show in the link.
http://67-72chevytrucks.com/vboard/s...highlight=tach

[mtchevytruck]

Originally Posted by Justins76

Anyone know if 73+ trucks use a shunt type ammeter?

I'm not familiar with the term shunt. From what i found 1973-75 used amp meters and 76-87 used volt meters.

[mtchevytruck]

Originally Posted by Justins76

This may be of help to you. Use your stock voltmeter and move the terminal post as show in the link.
http://67-72chevytrucks.com/vboard/s...highlight=tach

Good write up. Many years are different though. The 72' cluster did not have the upper terminal cut out in the plastic or have the printed circuit for a top terminal. What I had to do was cut the post off the back of the gauge that went to the left outer hole and I then inserted a double nutted screw with a terminal and wire attached to the back side of the cluster. Then I drilled a small hole through the white cluster case and ran the wire through to the upper terminal on the back of the gauge and nutted a wire terminal on to that. Works great.

I also had a seat belt warning light, brake warning light and oil warning light (and a 4x4 light option that wasn't used) on the 77' cluster and only a brake warning light on the 72' cluster. I just swapped the wires in the harness so the brake warning would function and left the rest alone eliminating them.

[72lb4x4]

Originally Posted by Justins76

Anyone know if 73+ trucks use a shunt type ammeter?

That's what I described in my earlier post above.

A shunt ammeter is actually a voltmeter. In fact, I've been told that a regular ammeter is actually a voltmeter but the shunt resistor is inside the body of the meter...

[Jonboy]

I added a voltmeter to the '74 tach cluster in my '74. Scot had done this previously, I just added the tach cluster. The truck originally had a clock, so he used the clock wiring to the voltage gauge. You pull the metal tabs out of the instrument cluster carrier, so there is no contact with the printed curcuit. The tabs on the back of the gauge are threaded (10-32, IIRC), and just run the 12V+ from one side to the fuse block, and ground to the other side. There is a ground strip on the left side cowl panel that can be seen when the cluster is out, that's where mine is run to.

[Bigb401]

Originally Posted by 78 Chevyrado

Volt meters connect to the hot wire and tell you the voltage present in a system. The volt meter is a closed loop all on its own and is built light since not much amperage runs through it at all

amp meters show you the amperage draw to the battery, which means ALL system current runs through the amp gauge. the amp gauge is inline with the main power wire. amp meters are built heavy because heavy current runs through them.

Volt meters are better IMO.

That's not true. These gm ammeters are shunted (in parallel) to the system current and charging system. All system current does not flow through (series) the ammeter
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