Ammeter works when key is off?

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Craig Burriss

Craig Burriss

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Ive been fighting the wiring in my 70 Duster for a while now and I think I’ve almost got it figured out. But one thing that scares me is the factory ammeter works when the key is set to the off position. Like when I turn the headlights on while the ign is off, the ammeter needle drops. I don’t want to kill my battery.
Is this normal or do I have something hooked up wrong. I already have a bunch of wiring diagrams but those aren’t helping me here.
Thanks
 
There is supposed to be a fusible link on the ammeter line under the hood, right near the firewall. It's job is to prevent your car from catching fire if a short should develop on that always live wire.
 
Craig Burriss said:
Ive been fighting the wiring in my 70 Duster for a while now and I think I’ve almost got it figured out. But one thing that scares me is the factory ammeter works when the key is set to the off position. Like when I turn the headlights on while the ign is off, the ammeter needle drops. I don’t want to kill my battery.
Is this normal or do I have something hooked up wrong. I already have a bunch of wiring diagrams but those aren’t helping me here.
Thanks
Click to expand...
Its normal, but I think you'll feel much better knowing why.

The ammeter is in the power feed from the battery.
There is another power feed that carries the alternator's output.
These two feeds join at a welded splice where power is distributed.

So a schematic for power supply and distribution looks like this.
upload_2019-3-13_18-58-58.png


Looking at the schematic, notice the wires that are connected to the battery's positive terminal.
All of those are at battery voltage unless interupted at a switch.

When a switch is closed, a circuit to ground is completed and the current will flow through the ammeter.
upload_2019-3-13_19-9-39.png


When the engine is running, the alternator produces power at a higher voltage than the battery. Therefore power flows from the alternator and does not show on the ammeter, except for what is needed to recharge the battery.
 
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AJ/FormS said:
There is supposed to be a fusible link on the ammeter line under the hood, right near the firewall. It's job is to prevent your car from catching fire if a short should develop on that always live wire.
Click to expand...
Yes there is usually a link in the battery feed, but not in the early years.
The purpose of the link(s) is to allow high loads for short periods of time but protect against the danger of a short to ground on otherwise unprotected wires and equipment.
Location of the link varied from year to year, sometimes within model lines depending on the options.

Fusible Links in Charging Systems with Ammeter
 
Your ammeter is a very useful tool when you understand what it shows.
Its too bad Chrysler labeled many of them "alternator" under the needle which confused many of us.
Its somewhat akin to how most alternator output terminals have BAT cast next to them.

In any event, once you understand the ammeter only shows current flowing to or from the battery, the readings should make sense.
If the needle shows high rate of discharge or charge, especially for any length of time, stop and figure out why. The scale is 40 amps discharge to 40 amps charge. Anything over 30 amps should get your immediate attention.
 
AJ/FormS said:
There is supposed to be a fusible link on the ammeter line under the hood, right near the firewall. It's job is to prevent your car from catching fire if a short should develop on that always live wire.
Click to expand...
That fuse is there so I guess I’m good until I change to a volt meter.
 
"Fuse" is confusing.
It's not really a fuse, in the conventional sense, and it's best not to ever replace the fusible link with a conventional fuse. The F-link is a slow-blow device like Mattax said , and allows short term overloads, where a fuse would just pop and leave you stranded.
I think we're all on the same page, but felt the need to clarify "fuse".
 
WARNING!!!! DO NOT depend on the infamous fuse link!!! For any kind of protection!!!!
 
67Dart273 said:
WARNING!!!! DO NOT depend on the infamous fuse link!!! For any kind of protection!!!!
Click to expand...
Iam thinking on running either a 10g or 8g wire from alt output to starter relay to alleviate some of the amp draw through the bulkhead connector and under dash after reading the article in this thread.What would you use instead of the fusible link. Working on 70 stock dart.
 
I think it's interesting what is "fused" and what things are not "protected".
Things that you don't want to ever stop working till the wires burn up...............
as it were.
 
ricks70dart said:
Iam thinking on running either a 10g or 8g wire from alt output to starter relay to alleviate some of the amp draw through the bulkhead connector and under dash after reading the article in this thread.What would you use instead of the fusible link. Working on 70 stock dart.
Click to expand...


I'm thinking that solenoid draw is not a big concern.
That's a temporary load, right?
Do I understand your question?
(Did not read the article)
Do it and fuse it if you want to.
The "Headlight Mod" is much more important.
 
adriver said:
I'm thinking that solenoid draw is not a big concern.
That's a temporary load, right?
Do I understand your question?
(Did not read the article)
Do it and fuse it if you want to.
The "Headlight Mod" is much more important.
Click to expand...
By running 10g wire from alt output to battery side of starter relay it then carries most of the load to charge battery instead of sending all through bulkhead connector were thing tend to melt down if Iam reading correctly.There saying to use a fuse link in line of 10 g wire
 
ricks70dart said:
By running 10g wire from alt output to battery side of starter relay it then carries most of the load to charge battery instead of sending all through bulkhead connector were thing tend to melt down if Iam reading correctly.There saying to use a fuse link in line of 10 g wire
Click to expand...

Oh. I see.
My bad for not reading the article.
You might want to put in a volt meter just to better keep an eye on things since that would "bypass" the AMP meter for charging current, I guess.
Maybe hang a small one under the dash in front of your left knee.
You know, a some people have run a wire through the bulkhead connector and eliminated the Packard type blade connectors for that load you are talking about.
But that probably is more wiring than you want to do.

That meter melt down is a point of big debate.
I think as long as your connections are good and tight on the back, the AMP meter is pretty reliable.
That's my experience, anyway.
 
adriver said:
Oh. I see.
My bad for not reading the article.
You might want to put in a volt meter just to better keep an eye on things since that would "bypass" the AMP meter for charging current, I guess.
Maybe hang a small one under the dash in front of your left knee.
You know, a some people have run a wire through the bulkhead connector and eliminated the Packard type blade connectors for that load you are talking about.
But that probably is more wiring than you want to do.

That meter melt down is a point of big debate.
I think as long as your connections are good and tight on the back, the AMP meter is pretty reliable.
That's my experience, anyway.
Click to expand...
Yes planning on little digital volt meter also
 
ricks70dart said:
Yes planning on little digital volt meter also
Click to expand...
There are tons of small digital meters available on e bay. I bought one when I was building a pid controller for my beer brew kettle. It has a inductive pick up coil for the amps so no current goes through the meter.

I bought these for my cars so I also have a usb charge port for my cell phone. It displays volts normally and displays charging amps when the phone is plugged in. Dual Ports 3.1A USB Car Cigarette Charger Lighter 12V/24V Digital LED Voltmeter | eBay
charger.jpg
 
toolmanmike said:
There are tons of small digital meters available on e bay. I bought one when I was building a pid controller for my beer brew kettle. It has a inductive pick up coil for the amps so no current goes through the meter. I bought these for my cars so I also have a usb charge port for my cell phone. It displays volts normally and displays charging amps when the phone is plugged in. Dual Ports 3.1A USB Car Cigarette Charger Lighter 12V/24V Digital LED Voltmeter | eBayView attachment 1715303234
Click to expand...


That is way too easy.
 
toolmanmike said:
There are tons of small digital meters available on e bay. I bought one when I was building a pid controller for my beer brew kettle. It has a inductive pick up coil for the amps so no current goes through the meter.

I bought these for my cars so I also have a usb charge port for my cell phone. It displays volts normally and displays charging amps when the phone is plugged in. Dual Ports 3.1A USB Car Cigarette Charger Lighter 12V/24V Digital LED Voltmeter | eBayView attachment 1715303234
Click to expand...
cool bought 2 thanks
 
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