Charging system road rage

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McDart

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So it seems the charging system in my 72 swinger is not charging. I've barely touched the surface on tracking down the issue and I'm already pulling my hair out. I hate electrical.
Dash gauge shows discharge when running (see pic). Obviously because its running but not charging, yes?
With engine running, I disconnected the negative battery cable.car died.
Took the alternator and voltage regulator up to the big box auto parts store and had them both tested. They both passed.
I repaired the connector on the power lead to the alternator and made sure I put me field and statter connectors on the right tabs.
Started up the car looked at the gauge is still show discharge. Disconnected the negative cable car died.

Pulling my hair out as I do not know where to go from here, where to look for the problem.The wires at the firewall connector for the alternator and engine harness look not so great and I like to replace this harness but I don't know where to go from here. And does anyone know what the blue wire with the red tracer at this firewall connector, the middle connector, goes to?
I would really, really like to start driving this car now that I have some of the small safety checks/repairs done.

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Put a volt meter on the battery, it's not good for electronics to pull the neg cable off while the engine is running, it causes large voltage spikes and can blow out transistors and other components.
 
Well first off, do you own a voltmeter and a test light?
The alternator itself is very simple to check.
One small wire has power from ignition, other finds its way to ground through voltage regulator.
Third,large wire makes its way to battery indirectly.
So,both small wires disconnected,key one,one will light the test light.
Connect that wire back to alternator.
Start car with voltmeter connected to battery.
Ground other terminal and watch voltmeter. It should increase.
Perform this and get back to us. No point going through anything else until you establish if alternator is good.
 
First take a big deep breath, and say ooooooommmmmmhhhhhh.

Feeling better now?

Without any other info the photo of your wire harness connector looks like it is toasted, that is where I would start.

You can download your wiring diagram from mymopar.com and trace out what wire goes where. Verify batery negitave to points on the wires for voltage.
 
Yeah those two big fat boys are what you wanna check out; they go to and from the amp gauge. In fact go to the gauge first, those terminals on the back of it have been known to come loose. If you need to work under the dash, be sure to disconnect the battery on account of there is very little room under there, and those two wires are always live.
 
McDart said:
. And does anyone know what the blue wire with the red tracer at this firewall connector, the middle connector, goes to?
Click to expand...
For this, you need to check the '72 Dodge or Plymouth Factory Service Manual like Dana mentioned. Back pages of the electrical section will be the diagrams and connector charts.
McDart said:
Took the alternator and voltage regulator up to the big box auto parts store and had them both tested. They both passed.
Click to expand...
OK. Maybe.
TJ's diagnoses approach is good. This will narrow down where the problem is.
I'll add some comments in the reposting below.

Tooljunkie said:
Well first off, do you own a voltmeter and a test light?
Click to expand...
The alternator itself is very simple to check.
One small wire has power from ignition [usually blue], other [usually green] finds its way to ground through voltage regulator.
Third, large wire makes its way to battery indirectly. [through the main splice]

So, both small wires disconnected, [turn] key on, one will light the test light. [or show battery voltage if using a meter]
Connect that wire back to alternator.
Start car with voltmeter connected to battery.
Ground other [alternator] terminal and watch voltmeter. It should increase.
Perform this and get back to us.

I wouldn't worry about the battery feed (heavy wire with fusible link) right now. It's obviously connected to the mainsplice since its running the car. That means the ammeter connections aren't the problem either.
 
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UPDATE
Thanks for the help guys, especially tooljunkie (you Canadian guys ARE alright, lol). I printed out your instructions and went out to the car (after having to buy a new battery for VOM) and followed your instructions. It was odd as volts didn't rise so i reconnected that wire and checked the positive post on the alt and it was only putting out 1v. WTF? Unplugged regulator, same thing. felt leads at back of volt gauge in dash (with car off), nice n tight. I started the car again and moved the wires at the firewall connector. BINGO! Since the wires at the plug were in crap shape anyways and other wires had been hacked, spliced longer, etc, I had already decided to order a new harness this morning from classic industries. I am a happy old dude now!
I really just needed to sit back, chill and let my brain work through it.
THANKS AGAIN!
 
McDart said:
felt leads at back of volt gauge in dash (with car off), nice n tight
Click to expand...
That's good they were tight.
With the car off or on doesn't make a difference when messing with those connection. The battery must be disconnected before putting anything metal near them. A wrench or a wedding ring on your finger, doesn't matter. Those wires are always hot as long as the battery is connected.

upload_2019-5-24_18-13-1.png

So if the battery is at 12.5 Volts, every wire up to the key switch, headlight switch, and brake light switch is 12.5 Volts.

The meter that is marked 40 to 40 in your car is an ammeter. It shows current flowing to or from the battery.
When the alternator is running, current will flow through the ammeter until the battery is recharged. Then it will show zero.

The positive field wire gets power when the key is in run.
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Dont mean to hijack this post.....
Does anyone have a 67 up instrument cluster out of the car?

I would like to know what the resistance is thru the ammeter.
Thanks
 
I have a spare rally ammeter down at the garage. Also a couple of 70s era Hawk aftermarket instrument clusters with ammeters.
Whether the reading from my digital multimeter will be even close to accurate with that little resistance is another matter.
My understanding is the run of the mill multi-meters aren't accurate enough if you're looking into conversion to a external shunt.
 
By the way DO NOT EVER pull a battery cable off a running engine, and it is not a valid check.

"The old wives tale" is that if the engine dies the alternator is bad"

WHY THIS IS WRONG

1.....If the system is charging it generates a voltage spike which can damage electronics

2...If the system is actually working but the engine dies, it might simply be that the idle is too slow and maybe lights are on, causing you to (wrongly) believe the system is not charging

3...If the alternator is partly bad (several bad diodes) the engine may continue to run and make you think "good" when in reality the 40A alternator may be only putting out 15A or such
 
Dana67Dart said:
Give it your best shot!
Click to expand...
And the results are...
Zero, Zed, Nada on the meter!
So less than 0.1 Ohms plus/minus accuracy of the meter which I'll look up later.

The meter with the alligator clips together. 0.1 to 0.2 ohms. So that's our baseline reading.
upload_2019-5-26_14-29-6.png

Hawk gage set.
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Same with the RAC gage set.
And the here's the rally ammeter.
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Here's a back view of the shunt.
upload_2019-5-26_14-32-20.png
 
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