1972 Ammeter Test
Thread Starter
Racer
Joined: Feb 2013
Posts: 364
Likes: 39
From: Sebastian FL
1972 Ammeter Test
Ammeter needle doesn't move on my 1972 BB, a/c, pw, pb, ps 'Vette. Charging system seems to work OK. When I got the car about 1 1/2 years ago it moved a little for a short time. Now I am checking it out. With battery connected and two leads off ammeter I read 12.4v on both. With engine running I read 14v on each. When I check resistance with wires off ammeter but ammeter in console I read 0 to .4 ohms resistance. When I connect 1 1/2v battery across the terminals, ( ammeter still in console but disconnected), the needle immediately goes full scale. Any thoughts on what is going on and how I can determine what to fix?
Thanks
Thanks
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
The meter obviously works. Locate the two orange fusible links in the ammeter circuit(one attaches to the horn relay and the other is under the wiper motor where two #12 wires are spliced together). Then check for continuity from the meter connection to the end of the appropriate fusible link.
Drifting
Joined: Oct 2005
Posts: 1,615
Likes: 150
From: Forth Worth TX
It's most likely the gauge. They are delicate and go bad with time/use. Not sure what it would cost to rebuild your original, but you can get a GM Restoration Parts Ammeter for the 1972-74 Corvette for about $60 on most of the Corvette parts websites.
http://www.restorationperformance.co...-oer%2C/Detail
http://www.restorationperformance.co...-oer%2C/Detail
Advanced
Joined: Oct 2010
Posts: 80
Likes: 2
From: near Nuremberg Bavaria
I'm with jnb5101 so far - do as he suggests.
You don't write under which circumstances you expect it to move, and it doesn't.
My ammeter hardly ever moves, too ('70 BB). But I know why: 1) I converted my headlamps to switching by relay (and picking up the headlamp current at the horn relay). And 2) I keep my battery charged full at all times (using a trickle charger if necessary). This removes the two main reasons for the ammeter showing a large deflection. Maybe some of this applies to your situation, also.
You don't write under which circumstances you expect it to move, and it doesn't.
My ammeter hardly ever moves, too ('70 BB). But I know why: 1) I converted my headlamps to switching by relay (and picking up the headlamp current at the horn relay). And 2) I keep my battery charged full at all times (using a trickle charger if necessary). This removes the two main reasons for the ammeter showing a large deflection. Maybe some of this applies to your situation, also.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Mid 80's Voltmeter from a pickup....bolts in fine....tie one of the wires to the + term, and of course the - to ground.....
long as you see ~13.5-14.8 with engine running, you are fine....
no second guessing....CASE CLOSED@@@@!!!!
long as you see ~13.5-14.8 with engine running, you are fine....
no second guessing....CASE CLOSED@@@@!!!!
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Thread Starter
Racer
Joined: Feb 2013
Posts: 364
Likes: 39
From: Sebastian FL
'72 Ammeter follow up
Ammeter needle doesn't move on my 1972 BB, a/c, pw, pb, ps 'Vette. Charging system seems to work OK. When I got the car about 1 1/2 years ago it moved a little for a short time. Now I am checking it out. With battery connected and two leads off ammeter I read 12.4v on both. With engine running I read 14v on each. When I check resistance with wires off ammeter but ammeter in console I read 0 to .4 ohms resistance. When I connect 1 1/2v battery across the terminals, ( ammeter still in console but disconnected), the needle immediately goes full scale. Any thoughts on what is going on and how I can determine what to fix?
Thanks
Thanks
Bumping the meter with a 1.42v battery causes the meter to go full scale in both directions. The resistance across the meter terminals is 0.5 ohms. I'm temped to take the meter apart but am not certain this is the problem, I don't mind having my meter rebuilt or getting a new quality replacement as long as I am sure this is the solution.
Thanks again.
Thanks again.
Could the problem be the meter? If not, any other leads?
Thanks.
2026 Loser of the Year
Joined: Sep 2013
Posts: 36,595
Likes: 7,042
From: New Or-leens Loo-z-anna
Use two jumper wires to connect the ammeter to another vehicle.....connect it in the engine bay where it will be easier to do.
The ammeter should rise on start-up and drop some once the battery is fully charged.
The ammeter should rise on start-up and drop some once the battery is fully charged.
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
If the meter deflects with a small voltage applied to it, how can the meter be bad? The resistance of the meter (0.5 ohms-I tested one a few months ago and got 0.2 ohms) is within measuring error. If the meter was burned, it would show an open circuit and infinite resistance.
It sounds like you have a bad connection that is limiting the current flow thru the meter. Measuring the voltage at the blk and blk/wht wires shows that the circuit is intact, but doesn't show resistance in the circuit. If there is a high resistance point (maybe only a fraction of an ohm) the current thru the meter will be limited. For example: the meter is 0.5 ohms, and if the circuit has a bad connection (read that as resistance) of 0.5 ohms, the meter will deflect half as much as it should. And if the bad connection is 1 or 2 ohms, the meter will hardly deflect.
You have a bad(corroded) connection or a loose wire. Disconnect the car's battery(remove the negative cable) and measure the resistance of the blk and then the blk/wht wire to the positive battery terminal. By doing so, you're testing all the connections in the circuit (especially the horn relay and the bulkhead connections).
It sounds like you have a bad connection that is limiting the current flow thru the meter. Measuring the voltage at the blk and blk/wht wires shows that the circuit is intact, but doesn't show resistance in the circuit. If there is a high resistance point (maybe only a fraction of an ohm) the current thru the meter will be limited. For example: the meter is 0.5 ohms, and if the circuit has a bad connection (read that as resistance) of 0.5 ohms, the meter will deflect half as much as it should. And if the bad connection is 1 or 2 ohms, the meter will hardly deflect.
You have a bad(corroded) connection or a loose wire. Disconnect the car's battery(remove the negative cable) and measure the resistance of the blk and then the blk/wht wire to the positive battery terminal. By doing so, you're testing all the connections in the circuit (especially the horn relay and the bulkhead connections).
Last edited by jnb5101; Nov 25, 2014 at 03:51 PM.
Melting Slicks
Joined: Jan 2014
Posts: 2,478
Likes: 254
From: Downers Grove Illinois
If the meter deflects with a small voltage applied to it, how can the meter be bad? The resistance of the meter (0.5 ohms-I tested one a few months ago and got 0.2 ohms) is within measuring error. If the meter was burned, it would show an open circuit and infinite resistance.
It sounds like you have a bad connection that is limiting the current flow thru the meter. Measuring the voltage at the blk and blk/wht wires shows that the circuit is intact, but doesn't show resistance in the circuit. If there is a high resistance point (maybe only a fraction of an ohm) the current thru the meter will be limited. For example: the meter is 0.5 ohms, and if the circuit has a bad connection (read that as resistance) of 0.5 ohms, the meter will deflect half as much as it should. And if the bad connection is 1 or 2 ohms, the meter will hardly deflect.
You have a bad(corroded) connection or a loose wire. Disconnect the car's battery(remove the negative cable) and measure the resistance of the blk and then the blk/wht wire to the positive battery terminal. By doing so, you're testing all the connections in the circuit (especially the horn relay and the bulkhead connections).
It sounds like you have a bad connection that is limiting the current flow thru the meter. Measuring the voltage at the blk and blk/wht wires shows that the circuit is intact, but doesn't show resistance in the circuit. If there is a high resistance point (maybe only a fraction of an ohm) the current thru the meter will be limited. For example: the meter is 0.5 ohms, and if the circuit has a bad connection (read that as resistance) of 0.5 ohms, the meter will deflect half as much as it should. And if the bad connection is 1 or 2 ohms, the meter will hardly deflect.
You have a bad(corroded) connection or a loose wire. Disconnect the car's battery(remove the negative cable) and measure the resistance of the blk and then the blk/wht wire to the positive battery terminal. By doing so, you're testing all the connections in the circuit (especially the horn relay and the bulkhead connections).
Melting Slicks
Joined: Mar 2005
Posts: 2,094
Likes: 298
From: Midlothian VA
What are your expectations?
Best response so far is "You don't write under which circumstances you expect it to move, and it doesn't."
Amp meter - not a volt meter.
Properly functioning amp meter installed on a properly working charging system will read ZERO. It goes negative when there is a discharge state (engine off and turn on the head lights) and it only goes positive when the battery is charging (usually for just a few minutes right after starting the car).
Best response so far is "You don't write under which circumstances you expect it to move, and it doesn't."
Amp meter - not a volt meter.
Properly functioning amp meter installed on a properly working charging system will read ZERO. It goes negative when there is a discharge state (engine off and turn on the head lights) and it only goes positive when the battery is charging (usually for just a few minutes right after starting the car).
Thread Starter
Racer
Joined: Feb 2013
Posts: 364
Likes: 39
From: Sebastian FL
ammeter
What are your expectations?
Best response so far is "You don't write under which circumstances you expect it to move, and it doesn't."
Amp meter - not a volt meter.
Properly functioning amp meter installed on a properly working charging system will read ZERO. It goes negative when there is a discharge state (engine off and turn on the head lights) and it only goes positive when the battery is charging (usually for just a few minutes right after starting the car).
Best response so far is "You don't write under which circumstances you expect it to move, and it doesn't."
Amp meter - not a volt meter.
Properly functioning amp meter installed on a properly working charging system will read ZERO. It goes negative when there is a discharge state (engine off and turn on the head lights) and it only goes positive when the battery is charging (usually for just a few minutes right after starting the car).
Melting Slicks
Joined: Mar 2005
Posts: 2,094
Likes: 298
From: Midlothian VA
From your initial post it appears the gauge works.
"connect 1 1/2v battery across the terminals, ( ammeter still in console but disconnected), the needle immediately goes full scale".
So, question; what happens when you turn on the headlights with the engine off? Gauge should go negative due to draw on your battery.
How much it goes negative depends on the size/capability of your battery and the type/draw of your current headlights.
"connect 1 1/2v battery across the terminals, ( ammeter still in console but disconnected), the needle immediately goes full scale".
So, question; what happens when you turn on the headlights with the engine off? Gauge should go negative due to draw on your battery.
How much it goes negative depends on the size/capability of your battery and the type/draw of your current headlights.
Melting Slicks
Joined: Mar 2005
Posts: 2,094
Likes: 298
From: Midlothian VA
So for reference:
When turning on the headlights with the engine off:
On both my 71's the needle only falls negative less than half way between the "0" and the first indicator line - that's not much - but easily visible. Moves close to the first indicator line if I go with the high beams.
Both with engine running the needle hangs at the right edge of the 0.
On my 72, engine off, the needle barely moves negative - even with the high beams. Starting the engine only pushes the needle positive ....barely...to just the right edge of the 0. Found it difficult to force much needle movement from the 72 meter. While a substantial battery + good charging system results in little demand I would expect a bit more needle deflection with the engine off but I'm not concerned. I know it works because when my alt failed several years ago it ran negative letting me know something was amiss.
Hope that helps.
When turning on the headlights with the engine off:
On both my 71's the needle only falls negative less than half way between the "0" and the first indicator line - that's not much - but easily visible. Moves close to the first indicator line if I go with the high beams.
Both with engine running the needle hangs at the right edge of the 0.
On my 72, engine off, the needle barely moves negative - even with the high beams. Starting the engine only pushes the needle positive ....barely...to just the right edge of the 0. Found it difficult to force much needle movement from the 72 meter. While a substantial battery + good charging system results in little demand I would expect a bit more needle deflection with the engine off but I'm not concerned. I know it works because when my alt failed several years ago it ran negative letting me know something was amiss.
Hope that helps.
Burning Brakes
Joined: Jul 2009
Posts: 1,240
Likes: 294
From: ESCONDIDO CA
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I've notice when my battery is new, the meter shows a higher charge.
As my battery has aged, not as much meter movement. I think the battery (2+years old) has less capacity to accept a charge.
As my battery has aged, not as much meter movement. I think the battery (2+years old) has less capacity to accept a charge.
Thread Starter
Racer
Joined: Feb 2013
Posts: 364
Likes: 39
From: Sebastian FL
Ammeter
If the meter deflects with a small voltage applied to it, how can the meter be bad? The resistance of the meter (0.5 ohms-I tested one a few months ago and got 0.2 ohms) is within measuring error. If the meter was burned, it would show an open circuit and infinite resistance.
It sounds like you have a bad connection that is limiting the current flow thru the meter. Measuring the voltage at the blk and blk/wht wires shows that the circuit is intact, but doesn't show resistance in the circuit. If there is a high resistance point (maybe only a fraction of an ohm) the current thru the meter will be limited. For example: the meter is 0.5 ohms, and if the circuit has a bad connection (read that as resistance) of 0.5 ohms, the meter will deflect half as much as it should. And if the bad connection is 1 or 2 ohms, the meter will hardly deflect.
You have a bad(corroded) connection or a loose wire. Disconnect the car's battery(remove the negative cable) and measure the resistance of the blk and then the blk/wht wire to the positive battery terminal. By doing so, you're testing all the connections in the circuit (especially the horn relay and the bulkhead connections).
It sounds like you have a bad connection that is limiting the current flow thru the meter. Measuring the voltage at the blk and blk/wht wires shows that the circuit is intact, but doesn't show resistance in the circuit. If there is a high resistance point (maybe only a fraction of an ohm) the current thru the meter will be limited. For example: the meter is 0.5 ohms, and if the circuit has a bad connection (read that as resistance) of 0.5 ohms, the meter will deflect half as much as it should. And if the bad connection is 1 or 2 ohms, the meter will hardly deflect.
You have a bad(corroded) connection or a loose wire. Disconnect the car's battery(remove the negative cable) and measure the resistance of the blk and then the blk/wht wire to the positive battery terminal. By doing so, you're testing all the connections in the circuit (especially the horn relay and the bulkhead connections).
Melting Slicks
Joined: Mar 2005
Posts: 2,094
Likes: 298
From: Midlothian VA
With the Negative terminal disconnected the resistance in the Blk to positive terminal is 0.005 ohms. The blk/white is the same- 0.005. This looks to me like the wiring is ok. I am beginning to think the meter is faulty even though it will deflect when a 1 1/2 volt battery is placed across the terminals.