Ammeter pegged...

[7milesout]

Guys,

First off, I don't know jack about electrical. The only way I manage to wire anything (in a car) is with a handful of fuses. I just keep miswiring until the fuses stop popping and then I've got it right.

As of late, an issue has started with my 72 Scamp. When I first fire it up, the ammeter will peg out. This has only happened about 3 times lately. When this pegging of the ammeter happens, it sends my AFR gauge to full rich (falsely), and the blinkers blink too fast. The actual time the blinker light is ON is OK, but the time the blinker light is OFF is too short.

I thought the AFR gauge was messing up, but no, it is related to the electrical system. I experimented this morning. I just let it go, to see what would happen. The AFR gauge stayed glitched until the ammeter fell back to the midway point on the gauge. Then the AFR gauge acted as if it "restarted" and began operating normal. The blinkers went back to normal at that same time too.

Have I got a bad altenator? Bad regulator? Help an electrical illiterate brother out before I fry something. Funny thing, my brother (before he passed away) was an electrician. I'm a mechanical engineer. My brother used to laugh his arse off at me when we would wire something up on a car. I miss those days.


7milesout

 

[67Dart273]

VERY FIRST THINGS YOU DO!!

1...Go to MyMopar and download a free factory shop manual. That manual and several others on that site were provided by the guys on here. Also on that site are aftermarket wiring diagrams, which are sometimes easier to follow but not necessarily accurate connector....by...connector

MyMopar - Mopar Forums & Information - MyMopar Tools/Reference

2....READ the Mad article. Even if you do not perform the mod, it gives you some understanding of problems with these girls

Catalog

3....GET a multimeter and montior battery voltage at startup and while this is happening so you know what the voltage is actually doing

4.....GROUND THE VOLTAGE REGULATOR. Remove the regulator, scrape clean the rear of the mounting flange and front of the flange around the bolt holes, as well as around the bolt holes at the firewall. Remount with clean hardware using STAR lock washers. Another member on here suggests using a separate grounding wire from a mounting bolt to engine block.......not a bad idea

5....Make CERTAIN the engine block is grounded to the body. One good way is to ADD a ground cable known as a "starter cable" (eyelet to eyelet) from the rear bolt hole on the driver's side head (look at the front passenger side, it is the same holes) to something such as the master cylinder mounting studs.


6.....IF the above steps settle the thing down, you are NOT DONE YET. These girls suffer from VOLTAGE DROP in the wiring which causes the voltage to run HIGH by some amount. To find out do this:

A.........Start and run the car at fast idle. Warm it up, and this is better done without the problem you describe showing up. In other words the ammeter should be more centered. Perform this test first with all accessories off, and again with lights, heater, etc running full.

Stab one meter probe directly into the battery NEG terminal. Stab the other into the mounting flange of the voltage regulator. Stab through any rust, paint, etc. You are hoping for a VERY low reading, the lower the better, and zero is perfect. Again, turn on the lights, heater, and check again

B..........With the engine stopped, turn key to "run." Now you need to find the closest thing to the voltage supply to the voltage regulator. This is probably the igntiion ballast resistor which branches off. You want the "high" side of the resistor,..........the one coming from the key. One side is likely two wires with one brown. Wrong one. Check voltage at both terminals. If they are both the same, your points are open in the distributor. "Bump" the engine until they close. Now one terminal of the resistor should be "same as battery" and the other will be low...........8---to---10V or so. NOW CONNECT your meter to that high side.

Stab your other probe directly into the top of the battery POS post. As with test "A" you are hoping for a very low reading. More than about .3V (3/10 of one volt) means you have a voltage drop problem in the harness THIS DROP CAUSES the voltage regulator to run over voltage by the amount of the drop. For example If the VR is properly operating at 14V and you have 1.5V in this test, then the battery will "run" at 14 + 1.5 = 15.5V which you do not want

 

[7milesout]

Wiring diagrams look like ancient Egyptian hieroglyphics to me. I'm gonna guess the grounding of the voltage regulator is likely. As I've been finding other corroded connections of late. I'll read the attached and check the grounding out. Thanks!

 

[Mattax]

When I first fire it up, the ammeter will peg out.

Which way? Charge or Discharge?
Pegged indicates 40 amps or more are flowing out of, or into the battery. Which is it?

Have I got a bad altenator? Bad regulator? Help an electrical illiterate brother out before I fry something.

As Del noted, having a voltage reading will help ID the problem, especially if its pegging to charge.

 

[Mattax]

Wiring diagrams look like ancient Egyptian hieroglyphics to me. I'm gonna guess the grounding of the voltage regulator is likely. As I've been finding other corroded connections of late. I'll read the attached and check the grounding out. Thanks!

Try not to give up before you start.
You don't have to guess.
See what the ammter guage indicate. Does it change with rpm? and if you can measure voltage with a meter, that will help immensely.
40 amps through that circuit will start to overheat stuff.
Uncontrolled votlage can also sometimes damage things. Disconnect the AFR reader for now.

 

[7milesout]

It pegs on the + side. And when I go to idle under these conditions, the gauge does come down. If I remember right, it doesn't make it back to the center, it's still on the + side, but not pegged at idle.

 

[Mattax]

OK. Plus indicates Charging.
So at lower rpm, when you see its still plus, its charging at a lower rate.

Can you see that on this diagram?

Power comes from either the battery or the alternator, whichever is at higher voltage.

 

[67Dart273]

It pegs on the + side. And when I go to idle under these conditions, the gauge does come down. If I remember right, it doesn't make it back to the center, it's still on the + side, but not pegged at idle.

Forgot to ask did you recently change anything? Like the alternator? or wiring? or the VR?

Pull the connector off at the VR and see if it goes to center or some left. This will tell you that you don't have a problem in the harness or inside the alternator (shorted brush)

 

[7milesout]

That's a good sketch. If the battery is supplying the amperage that's being consumed, the ammeter will move to the - side. Inferring that the battery is being depleted. That makes sense. And vice-versa. Since mine is going positive, it indicating the alternator is charging. That is what I understand from the sketch you pasted.

 

[7milesout]

No, I've changed nothing.

 

[Mattax]

You got it!

So at lower rpm, when you see its still plus, its charging at a lower rate.

There's two possible reasons for the extreme charging on a normal system.
1. Battery was very low, and sucked a lot of current from the alternator after starting.
2. The voltage regulator isn't controlling the output voltage. So with increasing rpm, the voltage goes up.
> a. One cause can be the regulator seeing a lower voltage than the rest of the system is at due to poor connections.
>b. Another cause is internal or wiring failure bypassing the regulation. Del just mentioned a couple of ways outside of the regulator that this can happen.

 

[67Dart273]

OK. Plus indicates Charging.

That diagram is wrong and frankly I believe it confuses the issue. The ammeter/ alternator wiring does not go through two separate connector. But the way that is drawn makes things difficult to read.

The "gist" though is that all loads and the alternator are on ONE SIDE of the ammeter. ONLY the battery is on the remaining side.

Whichever is more positive is what supplies power. If the car is not running, or is running too slow to charge, the battery is at a higher positive voltage than the alternator. The way the load current flows, causes the ammeter to deflect negative

If the alternator is charging and is capable of keeping up with the load, AND IF the battery is low enough that it "wants" a charge, then the alternator is more positive, and this causes the ammeter to deflect positive

If the battery is completey charged, if there are no harness issues, and if the VR is working properly, then the alternator output at 14V "floats" the battery and the ammeter remains centered. If a load is turned on, the VR jumps the voltage to maintain the 14V and the ammeter remains centered.

 

[67Dart273]

You got it!


There's two possible reasons for the extreme charging on a normal system.
1. Battery was very low, and sucked a lot of current from the alternator after starting.
2. The voltage regulator isn't controlling the output voltage. So with increasing rpm, the voltage goes up.
> a. One cause can be the regulator seeing a lower voltage than the rest of the system is at due to poor connections.
>b. Another cause is internal or wiring failure bypassing the regulation. Del just mentioned a couple of ways outside of the regulator that this can happen.

Which is part of the reason you need to check with a multimeter Could also be the battery has a bad cell

If you think the battery might be low (EG from sitting) charge it up with a charger.

 

[Mattax]

Cause 'a' may sound confusing. I didn't write that clearly.
Lets say the voltage at the regulator is 1 volt less than the alternator is putting out.
The regulator than provides more power to bring the output up to 14 V, which causes the alternator to really provide power at 15 Volts.

 

[ragtopfury]

Had a 69 roadrunner years ago go full charge and blew out the low beam headlights on the way home from the track. Disconnected the alternator and drove home on the battery and high beams. Alternator and voltage regulator both went bad. My guess is the alternator blew out the VR. I replaced both and upgraded to a dual field/electronic alternator & regulator.

 

[Mattax]

The ammeter/ alternator wiring does not go through two separate connector. But the way that is drawn makes things difficult to read.

Some years it does. My '67 does. I know '68 and '69 it doesn't. I agree, that may not be the clearest diagram but that makes his success in reading it even better. I forget what that was drawn for - maybe a '74 Charger.

 

[Mattax]

Had a 69 roadrunner years ago go full charge and blew out the low beam headlights on the way home from the track. Disconnected the alternator and drove home on the battery and high beams. Alternator and voltage regulator both went bad. My guess is the alternator blew out the VR. I replaced both and upgraded to a dual field/electronic alternator & regulator.

His '72 already has the regulator and alternator with two field wires.

 

[7milesout]

I should also mention, that it was a bit of a long crank this morning. Not horrible. Maybe 7 or 8 seconds. But I drove it yesterday. The sun finally came out so I cleaned it up yesterday and drove it a bit. Then cranked it up again this morning and drove it to work.

The battery *seems* to be OK. But I say that only because it actually cranks the car. It could be having an issue. I'm going to record the lunch crank up and (try to) post it in here to give you guys a visual. Regarding both the crank time and what the ammeter does. My tach died, but I'm not sure if it's related to this, or just old-n-crappy. I don't like the gauge, I ordered another gauge before this one even died. I'm working on a bracket for the new gauge.


7milesout

 

[Mattax]

Go look over the wires and connections from the battery to the firewall and the same for the alternator output to firewall and the alternator field wires to regulator.
Take pictures and post if you want.

Beg, borrow, or buy a voltmeter (multimeter is fine). This will eliminate a ton of guessing.

 

[ragtopfury]

His '72 already has the regulator and alternator with two field wires.

Wasn't sure of the change over year. But my point being, could be the alternator and/or the vr. And yes, as always, test before replacing parts blindly.

It's all good - I'm not going to get all pissy about it. LOL.

 

[7milesout]

I've got a multi-meter already. I'm pretty sure it has something to do with electronics...

 

[7milesout]

Lunch crank. You can see it went way high (not pegged) for maybe 10 seconds, and then dropped to normal when I wasn't looking.

… Trying to figure out how to attach a video …

 

[Mattax]

Lunch crank. You can see it went way high (not pegged) for maybe 10 seconds, and then dropped to normal when I wasn't looking.

… Trying to figure out how to attach a video …

Can't help with the video, but don't worry about it too much. It's pretty clear from your description.

I've got a multi-meter already. I'm pretty sure it has something to do with electronics...

Your already headed in the right direction!

Set it to V DC, or the V without squigley lines.
Clip or hold the black wire to a good ground or battery negative.
Use the red probe or clip to measure the voltage at the places mentioned earlier in the thread. Battery Pos. and alternator out are good places to start. Note the voltage engine off, and running. Slightly rev the motor using the throttle on the carb if you have to. Note if the voltage follows the rpm.

 

[7milesout]

Guys,

Sorry a bit of a delay. I got some pictures but was in the process of removing the radiator simultaneously. So no cranking and checking voltage while no radiator.

I'm not certain this is the Voltage Regulator. But if it is, it appears from the outside to be in good shape. I'm not seeing any corrosion.

Should I pull it off and look in more detail?

 

[Mattax]

That's the voltage regulator.
Any time you see a 'P' part number, that's a later Direct Connection part sold by Mopar Performance.
No particular reason to use a p-part voltage regulator on a '72, probably was just convenient to buy it.

It's a solid state regulator. If it doesn't work, replace it.
Corrosion is not likely at the regulator terminals but pull the wire connection plug and look.

The more likely places for corrosion is the grounding - and its prob fine from the looks of it.
Oxidation and poor connections are most likely at the ballast resistor, at the bulkhead connector, as well as the field wire connections on the alternator.

The ballast resistor itself has nothing to do with the circuit. It just that the wire to the regulator is often joined to the ignition terminal at the resistor connection.

What I'm saying about the ballast resistor connections is that they look like this when the terminal is removed from the connector.

Only difference will be the one you are looking at will both be blue insulated wires.
Power flows in from one wire and continues on to the next wire, which connects to the regulator. It's also possible on a '72 the wire to the regulator is joined at another location. This where having a factory diagram for the year is helpful - and I don't have a '72.