bad ammeter effect

[Citiyard]

Friend has had a problem with his '30 coupe deciding to stop on it's own without warning. We've been through the fuel and electrical system and everything looks OK. I noticed that his ammeter was not registering and he told me it's never worked right. Can a bad ammeter affect the way a car runs or is it just a gauge?

[Kurt in NJ]

The electric connection internally can be bad, usually indicated by the ammeter getting hot, and it can be burned out by a short, then nothing would work.

[jrelliott]

Have you checked the venting on the fuel cap. If there is not a vent will run for a while then quit for lack of fuel.

[Bill G]

Not just a gauge. It is an integral part of the whole circuit. A bad ammeter can most definitely effect how a car runs. On a 30, everything except the starter motor itself goes through the ammeter. The ammeter is in series with everything to measure how much current is being used and how much is offset by charging.


It could be a clue, but check all other wires and connectors for tightness and for any corrosion, including those connecting to the back of the ammeter.

[1955cj5]

Here is another place to look...

https://www.fordbarn.com/forum/showthread.php?t=329760

[rotorwrench]

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Not quite everything is directly connected to the ammeter circuit. It is connected to indicate generator output so that is it's main connection between generator and battery. The ignition and panel light circuits are connected through the load side of the terminal box if the 1929 service bulletin has been complied with. Horn and main lighting circuits are connected direct to the generator.

As was mentioned, if wiring had become loose or if a wire has shorted then the engine can quit. It's a good idea to check wiring every so often just to make sure all connections are tight and there is no damage to insulation in places that are sometimes problematic.

The reproduction ammeters leave a lot to be desired. I trust the old originals more.

[Fairlane514]

Does it turn off like a light switch, or slowly sputter and die?

May be a condenser getting hot and failing.

Does it cool down and start back up?

[Jerry in Shasta]

Bad amp gauges are also source of many fires. I open amp gauges and solider the circuit to the terminal post

[katy]

Originally Posted by Citiyard

Friend has had a problem with his '30 coupe deciding to stop on it's own without warning. We've been through the fuel and electrical system and everything looks OK. I noticed that his ammeter was not registering and he told me it's never worked right. Can a bad ammeter affect the way a car runs or is it just a gauge?

Try putting a jumper across the terminals of the junction block. That will remove the ammeter from the equation.

[nkaminar]

The jumper wire will also remove the ammeter from the circuit.

[Badpuppy]

Jumper won't remove the ammeter. It may be shorting to the tank. Jumper won't clear that.

[Citiyard]

Originally Posted by jrelliott

Have you checked the venting on the fuel cap. If there is not a vent will run for a while then quit for lack of fuel.

This has been checked and its intact .

[Citiyard]

Originally Posted by jrelliott

Have you checked the venting on the fuel cap. If there is not a vent will run for a while then quit for lack of fuel.

Originally Posted by katy

Try putting a jumper across the terminals of the junction block. That will remove the ammeter from the equation.

Will be looked into .

[Citiyard]

Originally Posted by Fairlane514

Does it turn off like a light switch, or slowly sputter and die?

May be a condenser getting hot and failing.

Does it cool down and start back up?

It does slowly sputter and die .

[Citiyard]

Loving the forum so far. Nice, knowledgeable people. Hard to come by it seems.

[jrelliott]

Please post the answer to your problem when you get it fixed.

[jeepguy1948]

Just my opinion (after 45 years as an industrial electrician) ammeters is general are a weak link in any electrical circuit especially when dealing with 6-12 volts. The ones made for automotive use are of very low quality and prone to failure because they can’t handle a lot of current for very long because the overheat and fry. I find that in an automotive type situation the ammeter can really slow down the battery charge. On a Model A, when the generator is swapped for an alternator more current is available further loading the ammeter so generally changing the ammeter to one of higher amperage readings is a good idea. I’m not saying that an ammeter is not of no use, I’m saying it’s a weak link. Personally, I leave them in place for appearance but bypass them and install a quality voltmeter (I get mine from Westach). If you know what to look for a voltmeter will tell you more about charge/discharge of the battery. You can argue all you want about how great it is to have but it’s still a weak spot in the system. The right option for an ammeter is to have one which uses a shunt that carry’s to load and actually provides voltage to run the ammeter (think about it this way; the oil pressure gauge will tell you the oil pressure without all the oil flowing through it, same with the temperature gauge.

[Rob Doe]

Citi,

I may be incorrect, but I'm thinking that if you jumper across the junction box terminals to bypass the ammeter, you should unhook the yellow and yellow / black stripe wires either at the ammeter or junction block and tape them off.

If the problem is an intermittent short to ground, then installing the jumper without unhooking the wires will not solve the issue??? Unhooking them at the terminal box would be the better solution than at the gauge. Then install the jumper between the two terminals.

If I'm wrong here, I hope to be corrected.

[jeepguy1948]

You are not wrong you are right on. That is the way to do it. I really don
T know if the gauge is his problem or not but talk seemed to wander over it that direction.