Factory Ammeter Troubleshooting/Diagnostic

Hi everybody,

Our mach 1 project is rolling along, we got the car started two days ago.

I noticed that when the engine was rolling, the rpm, oil press, water temp gauges all worked fine except for the ammeter gauge. (All gauges are stock from factory) (Car has the gauge harness from factory that runs to battery area)

Q1: Is there an easy way to test the ammeter outside the vehicle? (on a workbench lets say)

I have two mach 1 gauge clusters and would like to see if on both the ammeter is still operational. From that conclusion, I would then move on to check the wiring harness...

Thank you

Marco/Andrew

You'll rarely see the ammeter move in the car.

To test on the workbench, get a C or D cell battery (9V transistor will also do in a pinch), and use jumper leads and alligator clips: + to yellow wire side and - to red wire side. When connecting to the ammeter, just briefly touch one lead while the other is connected, as the gauge will peg. With that much voltage difference sustained for more than a few seconds, the gauge can easily burn itself up.

You'll rarely see the ammeter move in the car.

To test on the workbench, get a C or D cell battery (9V transistor will also do in a pinch), and use jumper leads and alligator clips: + to yellow wire side and - to red wire side. When connecting to the ammeter, just briefly touch one lead while the other is connected, as the gauge will peg. With that much voltage difference sustained for more than a few seconds, the gauge can easily burn itself up.

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Ok Thanks for the info!

Ill check it out

the gauge will just move slightly off center. if everything is in the car and hooked up. get in and watch the gauge carefully , turn the headlights on there will be a very slight deflection to D for discharge.

it isn't a volt meter it is a amp meter.

most people think its a volt meter and do not understand why it doesn't move much.

if that gauge reads off center then you have a major problem.

you can have the gauge converted to a volt meter there is a guy that refurbishes gauges.

the gauge will just move slightly off center. if everything is in the car and hooked up. get in and watch the gauge carefully , turn the headlights on there will be a very slight deflection to D for discharge.
it isn't a volt meter it is a amp meter.

most people think its a volt meter and do not understand why it doesn't move much.

if that gauge reads off center then you have a major problem.

you can have the gauge converted to a volt meter there is a guy that refurbishes gauges.

Click to expand...

That's him ::thumb::

http://www.rccinnovations.com/index.php?show=menu-mustang-all

I will try it next weeks and send him one of my cores...

the gauge will just move slightly off center. if everything is in the car and hooked up. get in and watch the gauge carefully , turn the headlights on there will be a very slight deflection to D for discharge.

it isn't a volt meter it is a amp meter.

most people think its a volt meter and do not understand why it doesn't move much.

if that gauge reads off center then you have a major problem.

you can have the gauge converted to a volt meter there is a guy that refurbishes gauges.

Click to expand...

By off center, what do you mean. I just noticed it quickly, the needle pointing straight down. Yes, we didn't have everything hooked up when we started the engine.

thanks for the info!

The needle may move perhaps half of a needle's width towards discharge with the headlights on, brake lights on, door open, etc.

Good read!

Have been wondering why my meter does not move.

From what I garner from the conversation is if the meter

moves much at all or deflects from center you have Major

problems.

Thank you 72.

mike

The latest Dec issue of Mustang Monthly has an article on gauge restoration. They mention that since ammeters typically failed and started fires, its better to disconnect and bypass them. They seem to be talking about the earlier 60's mustangs so dont know if this also applies to the 71 - 73. Seems like ford would have corrected something thats a fire hazard.

If I understood correctly this gauge is working properly if there is only a slight lean towards either D or C. :huh:

If there's a major lean(deflection) or it doesn't reset to the center position then we might have problems running it and we should disable or substitute my other gauge cluster.

Thank you for your understanding!

Marco/Andrew bros

The latest Dec issue of Mustang Monthly has an article on gauge restoration. They mention that since ammeters typically failed and started fires, its better to disconnect and bypass them. They seem to be talking about the earlier 60's mustangs so dont know if this also applies to the 71 - 73. Seems like ford would have corrected something thats a fire hazard.

Click to expand...

Unfortunately, all ammeters from 1966 through 1973 are of the same design: unfused wiring directly from the alternator and starter solenoid battery post.

If I understood correctly this gauge is working properly if there is only a slight lean towards either D or C. :huh:

If there's a major lean(deflection) or it doesn't reset to the center position then we might have problems running it and we should disable or substitute my other gauge cluster.

Thank you for your understanding!

Marco/Andrew bros

Click to expand...

Pretty much correct. Although...Midlife (my 1966 GT fastback) had an ammeter that would swing wildly negative. I could push/pull wires on the under-dash and get it to go back to normal. It turns out that was not the problem, but a molded connector at the starter solenoid. If either molded connector for the main alternator to battery line was flakey and had a bit higher resistance, more current would flow through the ammeter than normal. I found that by tugging on the molded connectors near the starter solenoid, I could duplicate then eliminate the high current reading on the ammeter. So...just because the ammeter does swing high one way or another does not necessarily mean something is wrong.

I've also helped troubleshoot a 65 at an MCA National event, and the ammeter worked great: swings a good 1/4 gauge deflection down then up, depending upon what was on and the engine idle speed. Now then, the 65 ammeter was an inductive device, and I've heard that these are much better for deflection than the direct wired ammeters.

Thank you very much for the info midlife!!

Marco/Andrew

If I understood correctly this gauge is working properly if there is only a slight lean towards either D or C. :huh:

If there's a major lean(deflection) or it doesn't reset to the center position then we might have problems running it and we should disable or substitute my other gauge cluster.

:whistling:

Thank you for your understanding!

Marco/Andrew bros

Click to expand...

The amp gauges on the 71-73 were a shunt type ,All the altenator current does not pass through the meter. so they move a very small amount.