Ampmeter question

mrlaser

mrlaser

Senior Member
The ampmeter needle in my 1951 Ford v8 is always in the charge position though all else is working normally. It appears that the needle is stuck in its position. This is whether or not the car is running or the battery is connected. I have a another meter, but the gauge cluster is difficult to get to. I did hook up a small 6 volt bulb in series with another gauge (as shown in the diagram) at the battery. Making and breaking the connection causes the bulb to illuminate but there is no movement of the ampmeter needle. Could this be due to the small size of the test bulb? I have repeated this test with 2 NOS ampmeters. Not sure how to proceed. BTW, it is a 6 volt pos ground system with a new wiring harness. Thanks for any advice.
 

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If wired properly take the yellow wire off of the B terminal on the voltage regulator and run it thru the loop on your spare amp meter and hook it back up to the B terminal. Turn on the lights with motor off and you should see movement on the spare meter. (Could be charge or discharge depending on which end of the spare meter you ran the wire thru). If there is movement either the dash gauge is bad or a wiring issue.

Hope this helps,

Tom
 
If the needle sits off of the center/zero mark with the battery disconnected, and there is no movement with lights on/off when battery is connected, it is certain that the meter movement within the gauge is stuck.

It is definitely possible that a small bulb would not draw enough current for you to see the replacement ammeter needle move. Try using a headlight bulb as the load; that will definitely move the needle.
 
I am not familiar with what type of ammeter is in a 51. There are loop ammeters, wired in ammeters and voltage indicators. Looking at the wiring diagrams, it looks like a loop type. If it is the loop type the test in the OP are a bit baffling. Would it be possible to post a photo of the ammeter in question? (the wiring diagrams do not always match up with production).

Found some photos of F-1 gauges, and they are the loop type. Also found 1 photo that claims to be of a 51 passenger car, and it would be the wired, shunt type.
 

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The ampmeter is not the loop type. It is exactly as pictured above. I will try to find a 6 volt headlight bulb to retest. If connected as in the diagram and the wires were reversed from normal, the needle movement would just show a charge when put under a load, correct? Thank you all for your help.
 
Mr.Laser

In my response #2 since you don’t have a loop amp meter. Remove the yellow wire on Bterm of the voltage regulator and attach it to one side of your amp meter. Then connect a piece of wire from the other side of the meter to the B terminal. Them turn on the lights.

You have put the meter in series with the load as the diagram shows.

Feel free to call 856-912-2711

Hope this helps,

Tom
 
Thank you Tom. I will try that and let you know the results. It's not so easy to find 6 volt headlights in the local parts houses.
 
Well, I did as suggested by Tom, but the spare ammeter must be defective as well. The headlights come on normally, indicating there is current flowing through the shunt in the meter, but the needle doesn't deflect to either the positive or negative. I also tried tapping on the back of the ammeter that is currently installed in the instrument cluster, but the needle remains stubbornly fixed out of alignment. I may try a modern SW shunt type gauge to check the system further. Any additional ideas would be welcome. Thank everyone.
 
If the needle indicates off-center AND doesn't move AT ALL, no matter the charge or the load applied, something is likely bent hindering any movement. DD
 
Don't think the setup Tom posted will work. The ammeter has to be set up where all of the current going to and from the battery passes through it (one of the reasons they can be a safety issue, but that is another topic). It is looking at the direction the current is flowing to and from the battery. It needs to be connected between the main power wire from the battery to the rest of the system. When the lights are turned on for example, the current would be flowing from the battery to the lights with the ammeter in-between and would deflect toward the discharge side. If it was all connected up with the generator and VR and the vehicle was running (without the lights or other heavy loads turned on) the ammeter would deflect toward the charge side (current flowing toward the battery).

If you are wanting to use the car as a test rig, might try connecting a wire from the battery side of the starter solenoid. Remove the main power wire on the starter solenoid (normally the large yellow wire) that goes to the instrument panel. Connect that wire to the ammeter. Now connect a new wire from the ammeter back to the starter solenoid. Now try the headlight test and/or start the vehicle and check it out.

This puts the ammeter in the main current path to and from the battery and the ammeter will indicate current flow direction.
 
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The original stock set up is the wire on the B terminal feeds the amp meter on the dash. By putting his meter in series with the wire as I described he should see some movement on The meter. Depending on how it was hooked up it could show charge or discharge.

If it moves the dash amp meter is either wired wrong or defective.

I am assuming that the original amp meter did work at one time.

Tom
 
Jersey Devil said:
The original stock set up is the wire on the B terminal feeds the amp meter on the dash. By putting his meter in series with the wire as I described he should see some movement on The meter. Depending on how it was hooked up it could show charge or discharge.

If it moves the dash amp meter is either wired wrong or defective.

I am assuming that the original amp meter did work at one time.

Tom
Click to expand...

The B terminal connection to the ammeter and the Battery connection to the ammeter should be on opposite sides. There shouldn't be any current flow to or from the B terminal unless the engine was running. Maybe the assumption was the car would be running during the test, which would work. If you use the starter solenoid connection the engine does not have to be running.
 
JSeery,
Would connecting my extra ammeter to the currently installed ammeter's posts (without actually removing its connections) ie adding a second ammeter, provide the necessary current pathway? There would be two gauges actually connected to the wiring harness leads
I do think the currently installed ammeter's needle is bent and as a result, not moving. I just wish that I had noticed it before assembling the dash. It is in an inaccessible spot for someone who is no longer very flexible. I can just get to the lugs on the meter while in an unnatural position.:)
 
As long as they are connected in series should be fine. Is it that easy to get to the wiring under the dash? Connecting it at the starter solenoid is really the same thing. The wire from the solenoid should go directly to the ammeter in the dash, so you are just talking one end or the other of the same wire.
 
No. It's very difficult ( at least for me) to get to the back of the installed ammeter. I will try the alternative that you have suggested. Thank you for your help.
 
Mr Laser.

If you read responses #8 and 13 and start the engine there is no need to get under the dash..

You had the answer to your inquiry days ago. If the dash amp meter needle is bent you know what you have to do.

Tom
 
Jersey Devil said:
Mr Laser.

If you read responses #8 and 13 and start the engine there is no need to get under the dash..

You had the answer to your inquiry days ago. If the dash amp meter needle is bent you know what you have to do.

Tom
Click to expand...

Or you can connect it to the starter solenoid and not have to start it. :)
 
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