Electrical gremlin

-
Pumpkinduster

Pumpkinduster

Well-Known Member
Joined
Nov 25, 2018
Messages
141
Reaction score
40
Location
Oregon
Hey all,
I have been trying to determine where my issue is and coming up with no luck. 74 Duster, The car was running the other day, shut it off and when to start it 10 minutes later and I have no power in the car, no dome light nothing. So after an hour of testing under the hood and at the bulk head i called it quits for the night. The fusable link is fine, I have 12v at the positive inside the car at the bulk head. I try to trace where I thought the positive ran from there and it lead me to the ammeter, so for some reason a decided to smack the dash. What do you know the light came on and the car started. So I tore the gauge cluster out and tore it all apart to see what the issue is, the ammeter had corrosion all over and obvious burning on it. The positive post was loose to the base so I though this is the issue for sure.

Now that I am thinking about it, that cant be the issue can it, since the ammeter has nothing to do with the rest of the electrical how would that cause the issue. Did a bandaid fix and put a little JB weld on the post to the base on the backside and cleaned all connections up. And now I'm back to no power in the car.

I have 12v coming in the car at the bulk head and 12v at the ammeter, no where else I have tested.
I tested at the fuse box on the Red w/white strip and smaller red, I have checked the seat belt module (im pretty sure that is what the 2 connector little box under the dash is) and still nothing. Also tested at the connectors going to the steering column and same no power.

Where should I test next? Also the little control module is this needed, I found the capacitors are pretty corroded and breaking apart.
 
Last edited:
Also I wanted to note that the Ammeter gauge has always worked. I know the source of the corrosion and that is being addressed already, but the car is now garaged so its not a new issues and can tell its an older leak at the wipers.
 
Electrical gremlin
0de1b35c89c8306d2cfbc1d3f20beda1.jpg?ixlib=rails-2.1.jpg


Sorry. Carry on!
 
Pumpkinduster said:
Only pulling from the post with the positive feeding it.
Click to expand...
If you only have power at one post and it's fully wired stock, you have a bad connection, or, a bad ammeter. The juice needs to flow through that ammeter without resistance. You may have accidentally insulated one of the connections with your JB weld epoxy. The terminals and connections need to be completely clean and tight.
 
cudamark said:
If you only have power at one post and it's fully wired stock, you have a bad connection, or, a bad ammeter. The juice needs to flow through that ammeter without resistance. You may have accidentally insulated one of the connections with your JB weld epoxy. The terminals and connections need to be completely clean and tight.
Click to expand...

ok good to know I have one I’m going to buy today to replace it anyways so we will see I if that takes care of the issue
 
Pumpkinduster said:
Now that I am thinking about it, that cant be the issue can it, since the ammeter has nothing to do with the rest of the electrical how would that cause the issue.
Click to expand...

Pumpkinduster said:
Also I wanted to note that the Ammeter gauge has always worked.
Click to expand...

The ammeter is just another link in the system. If it got corroded and there were poor connections, the resistance converted some of the electricity flowing through into heat. That could hae been sufficient to loosen the metal to metal press fit between the plate and the studs.

The needle doesn't touch the metal plate. It reacts to the magnetic field created by the current flowing through the plate. So the needle can still work, even though there is a poor connection.

Get another meter, or if you want, some people have fixed these. First thing is to make the stud connections to the metal plate solid. Then make sure the insulation and studs are solid.

There's a post showing how someone did this. I'll try to find it.
 
Here's the link. Your ammeter is probably a little different. The important point is make a very solid electrical connection between the studs and the metal plate. it may have to occassionally handle 40 amps, and will routinely handle 10-20 amps - although for only a minute or so.
Bullet-Proof Your Ammeter (A 'How To')

After you make the fixes and get votlage at all the places that should be hot, remember that does not guarentee good connections.
To test for low resistance connections, you will have to flow current through the circuit of interest and see of there is any measurable voltage drop.
 
Mattax said:
The ammeter is just another link in the system. If it got corroded and there were poor connections, the resistance converted some of the electricity flowing through into heat. That could hae been sufficient to loosen the metal to metal press fit between the plate and the studs.

The needle doesn't touch the metal plate. It reacts to the magnetic field created by the current flowing through the plate. So the needle can still work, even though there is a poor connection.

Get another meter, or if you want, some people have fixed these. First thing is to make the stud connections to the metal plate solid. Then make sure the insulation and studs are solid.

There's a post showing how someone did this. I'll try to find it.
Click to expand...
So just for testing what would happen if I put a 30amp breaker in replacement if of the ammeter? I feel like I’ve heard of people removing them completely from the system(not looking to do that) just curious to by pass it to make sure I get all my power before I spend more money then needed.
 
A 30A is likely not enough, when charging hard the line will be flowing more current. Might get by for a short time

Pumpkinduster said:
that cant be the issue can it, since the ammeter has nothing to do with the rest of the electrical how would that cause the issue. .
Click to expand...

The ammeter in these girls has everything to do with the ENTIRE electrical system, except for the main starter power

You need to get yourself a 74 factory service manual. There should be one "coming up" at Mymopar as I sent him one. Meantime the electrical system IS DIFFERENT than other years, and I've posted alink to a reduced file for ONLY the electrical section of the manual, here:

Free service manuals

Go to post 64 on page 3. Click the black icon in the box and 'save as' Its a pdf

Pleas go here and read this article which points out the problems with these girls ammeters

Catalog

On that page is this simplified diagram of main power distribution

amp-ga18.jpg


Notice the "welded splice" in the large black ammeter wire. This is under the dash, not far from the ammeter, wrapped up in the harness. That splice branches off and receives power from the alternator, and feeds power to the headlights, the fuse panel "hot" buss, and the ignition switch main feed. Some years, one or two other feeds.

Since you have all this apart, I would carefully take the ammeter apart, "if you can solder" and silver solder the studs to the shunt. You will need to get this all clean and use proper flux. Some of us bypass the ammeter and convert to a voltmeter
 
Damn near every electron in that car flows thru the ammeter. Bypass the p.o.s. ammeter by bolting the connectors to the same stud and bypass the bulkhead connector (search the site) or risk burning your car down.

A volt meter has, in my opinion, more value in info provided, anyway.
 
67Dart273 said:
A 30A is likely not enough, when charging hard the line will be flowing more current. Might get by for a short time

The ammeter in these girls has everything to do with the ENTIRE electrical system, except for the main starter power

You need to get yourself a 74 factory service manual. There should be one "coming up" at Mymopar as I sent him one. Meantime the electrical system IS DIFFERENT than other years, and I've posted alink to a reduced file for ONLY the electrical section of the manual, here:

Free service manuals

Go to post 64 on page 3. Click the black icon in the box and 'save as' Its a pdf

Pleas go here and read this article which points out the problems with these girls ammeters

Catalog

On that page is this simplified diagram of main power distribution

View attachment 1715785658

Notice the "welded splice" in the large black ammeter wire. This is under the dash, not far from the ammeter, wrapped up in the harness. That splice branches off and receives power from the alternator, and feeds power to the headlights, the fuse panel "hot" buss, and the ignition switch main feed. Some years, one or two other feeds.

Since you have all this apart, I would carefully take the ammeter apart, "if you can solder" and silver solder the studs to the shunt. You will need to get this all clean and use proper flux. Some of us bypass the ammeter and convert to a voltmeter
Click to expand...

so how are you by passing it then? I already have a voltage meter in the car and never look at the ammeter so if it doesn’t work I’m good with that too. This car is by no means a restored oem car lol
 
Pumpkinduster said:
So just for testing what would happen if I put a 30amp breaker in replacement if of the ammeter? I feel like I’ve heard of people removing them completely from the system(not looking to do that) just curious to by pass it to make sure I get all my power before I spend more money then needed.
Click to expand...
Not really sure what you're trying to test out.

Are simply trying to confirm the ammeter is where the break in the line is?

For that there are two simple tests.
One is what you did. If there is battery power on one post, and not on the other post, there's a break.
All of the wires connected to the battery should be hot at all times. That includes two or three of the fused circuits, the wire up to the alternator, the output wire from the alternator, and power to the horn (not shown on this schematic).
upload_2021-8-23_23-5-19.png


The other is disconnect the battery and check for continuity between the two posts.


The ammeter simply shows if power is flowing through that line. In other words whether the battery is charging or discharging.
At all other times its at zero. If you want a quick test, bolt the wires together. Safest to do this on one of the ammeter posts. Its critical to keep the wires and terminals from accidently grounding. If you goof and ground the battery, the fusible link will go poof!
 
jos51700 said:
Damn near every electron in that car flows thru the ammeter. Bypass the p.o.s. ammeter by bolting the connectors to the same stud and bypass the bulkhead connector (search the site) or risk burning your car down.
Click to expand...
Simply not true.
The battery doesn't run the car. The alternator does. The ammeter only shows whether the battery is charging or discharging. Only during those times electrons flow through the ammeter. In fact thats what ammeters measure, rate of electrons moving through a circuit.

Nor is the ammeter a source of car fires. In fact it shows when a high current situation is occuring in that line - which may alert the operator to a situation where something may melt or fail (like the battery or a connection). A voltmeter can't show that. It provides good clues to other situations. Neither one is better or worse, just different.
 
Last edited:
Alright well it’s clear the ammeter is the issue. Thank you for all the advice I have it fired up and will determine if I want to replace it right now or wait until this winter when I start my other laundry list of fixes
 
The battery doesn't run the car, the alt does? Try starting a car that has an alt but no battery.
 
The alternator provides the necessary power to run the car. Battery is there to carry the intermittent loads and is replenished by the alterntor.
Ammeters arent useless, but are limited to what they do.
Voltmeter shows voltage before,during and after starting a vehicle, making it a diagnostic tool for the battery,starter and alternator.

i was bypassing ammeters before the internet told me to.
 
This is the 3rd thread on the same subject in about a month. The corrosion is due to a water leak, wiper pivot or windshield gasket. Replacement gauge or placing both wires on one stud isn't a fix. Bolt the wires together off the gauge? Since the same water leak damages the headlight switch also, fix the water leak. Consider a handmade shield cut from butter tub, milk jug, whatever.
 
Mattax said:
Simply not true.
The battery doesn't run the car. The alternator does. The ammeter only shows whether the battery is charging or discharging. Only during those times electrons flow through the ammeter. In fact thats what ammeters measure, rate of electrons moving through a circuit.

Nor is the ammeter a source of car fires. In fact it shows when a high current situation is occuring in that line - which may alert the operator to a situation where something may melt or fail (like the battery or a connection). A voltmeter can't show that. It provides good clues to other situations. Neither one is better or worse, just different.
Click to expand...

Lessee.....The ammeter only shows charge/discharge. Agreed. What discharges said battery?
Every electrical function in the car, save the alternator. Thus, what I said is true. In order for the ammeter to function at all, "Damn near every electron in that car flows thru the ammeter" Doesn't matter if it comes from the alternator or the battery.

Proof?

Disconnect either side of the ammeter and leave it hang (insulated from ground, natch). Tell me what still works.....

RedFish said:
This is the 3rd thread on the same subject in about a month. The corrosion is due to a water leak, wiper pivot or windshield gasket. Replacement gauge or placing both wires on one stud isn't a fix. Bolt the wires together off the gauge? Since the same water leak damages the headlight switch also, fix the water leak. Consider a handmade shield cut from butter tub, milk jug, whatever.
Click to expand...

This is probably the best advice on the matter I've ever seen, and I never once considered it. Thanks!!
 
You must log in or register to reply here.
-

Back
Top