Erratic Ammeter

[DartGTDan]

My buddy's '63 Dodge 440 (383, 4-bbl, A/C, auto) has been having an issue. He claims that when he drives with the headlamps on the ammeter goes to full charge, drains the battery, and destroys the voltage regulator. Driving with the headlamps off, the ammeter shows just slightly to charge (which is what I would expect).

He has an old analog bench top volt meter (from Radio Shack) and made the following voltage measurement with the engine at normal operating temperature across the battery terminals measures ~16V.

We then swapped a known good battery from another vehicle and made the same measurement across the battery terminals. Again, it measured ~16V.

With the engine running (headlamps on or off) the ammeter is very rapid and erratic (see the video here ).

Where do we begin?

 

[Mattax]

My guess. The voltage regulator is supplying too much current to the field. Either because something is wrong with the regulator, or there is resistance in the circuit before the regulator. In either case, the result is the field supplies enough current that the alternator's output is 16 Volts. The battery will try to charge more when subjected to 16 volts, hence the current flow seen on the ammeter, but the actual result will be to cook the battery - boiling off the acid. The rapid ammeter movement makes me suspect the regulator itself.

Normal charging will be moderately high after start up, then dropping to zero after a few minutes of driving. What happens is the battery discharges during start. Once the engine is running, the alternator becomes the power source. As long as the alternator's voltage is higher than the battery's, current flows from the alternator. A portion goes to the battery until its fully charged. That's it. The ammeter only shows the portion going to the battery. As long as the alternator output is around 14 Volts, the battery will draw virtually nothing once its fully charged. The battery will temporarily read over 13 volts for a few seconds after the engine is turned off.

Where to begin?
I'd begin by taking a voltage reading at the input side of the voltage regulator. If its 14 volts, and the alternator is putting out 16 Volts, the problem is in the circuit. If both are 16 volts, I'd look in the voltage regulator.

 

[67Dart273]

There are several things this could be. Those here who know me know that I "HATE" throwing money/ parts at a problem. But in this case I'd try a new voltage regulator pretty quickly

Some other ideas:

1....READ the MAD article. Even if you don't do the mod, this presents an overview of "what is wrong" with many of these girls

Catalog

2....Perform my (posted many times LOL) voltage drop test. You can have drop both in the ground circuit AND the ignition / supply circuit

A.....Ignition drop: With engine stopped, key in "run" position, hook multimeter to VR "ign" terminal, hook other terminal to battery POS terminal. You are expecting a very low reading, the lower the better. Anything over .3V (3/10 of one volt) go looking for trouble

B....Ground. Run this test with engine running fast, battery "normalized" and first with accessories off, and again with lights heater, etc on

Stab one probe into the mounting flange of the VR. Stab the other into the top of the battery NEG post. Again, you are hoping for a very low reading, zero is perfect

 

[67Dart273]

There are several things this could be. Those here who know me know that I "HATE" throwing money/ parts at a problem. But in this case I'd try a new voltage regulator pretty quickly

Some other ideas:

1....READ the MAD article. Even if you don't do the mod, this presents an overview of "what is wrong" with many of these girls

Catalog

2....Perform my (posted many times LOL) voltage drop test. You can have drop both in the ground circuit AND the ignition / supply circuit

A.....Ignition drop: With engine stopped, key in "run" position, hook multimeter to VR "ign" terminal, hook other terminal to battery POS terminal. You are expecting a very low reading, the lower the better. Anything over .3V (3/10 of one volt) go looking for trouble

B....Ground. Run this test with engine running fast, battery "normalized" and first with accessories off, and again with lights heater, etc on

Stab one probe into the mounting flange of the VR. Stab the other into the top of the battery NEG post. Again, you are hoping for a very low reading, zero is perfect

3....VR MUST be grounded. Remove, scrape around bolt holes on firewall and back of VR and remount using star lock washers

4...General causes of drop. Again, the MAD article is a source, the diagram they have there is a good simplified view of the main power distro:

Drop generally occurs at ANY terminal, but there is usually about THREE or FOUR points "in" any "one" terminal!!! Take, EG, one terminal in the bulkhead connector: You have the (1) wire crimp on the firewall terminal......(2) the terminals "connection" itself, and (3) the wire crimp on the passenger compartment side. THAT ONE TERMINAL then has actually 3 points for "drop." That wire (big red) goes to the ammeter, you have about 4 fail points right there, the wire end terminals, the ammeter stud connections, etc etc, and out the BLACK ammeter wire to the WELDED SPLICE. "Tuck that" away for last, because rarely, they DO fail!!!! Next onward to your ignition switch.......You have (1) the crimp at the switch connector terminal feeding the switch, (2) the termination between the connector and switch, (3) the contacts in the switch (which may count as TWO) and (4) the IGN1 terminal at the switch, (5) the connection between it and the connector, and (6) the crimp on the the ignition wire (dark blue IGN1) coming out of the switch, and then THREE more going back out through the bulkhead connector!!!!!

The "point" is you have all these series points where failure(s)...(s) can occur and add up.

THE VOLTAGE YOU MEASURE in the voltage drop test is ADDED to a properly working VR, AKA if you show 2v drop, and the VR is properly working at 14, then your battery will "see" 17V!!

 

[67Dart273]

"The actual" problem............is likely a bad VR if it's the original "relay" type, or a bad connection in the post above, or bad alternator. The "functional" circuit path for field wiring is:

Battery.........fuse link.......bulkhead connector..........ammeter........welded splice........ignition switch..........bulkhead connector (dark blue)........and out to the VR

BAD CONNECTIONS IN THE output side of the alternator:

Alternator.........big black wire...........bulkhead connector.........to "welded splice......"..........to ammeter.........out bulkhead connector (big red) to fuse link and batteryl

ALTERNATOR ITSELF: Sometimes vibration can cause the stator windings to rub against themselves and rub the wires raw. Have him run the car "in the dark" and look at the alternator as you run the engine at different RPM and rev it. A "lightning light show" in the windings means "the alternator is done."

 

[67Dart273]

First one of these problems I found was "about" 1970-72 in the apt parking lot of a friend, working on his 68RR. At the time I owned a 69 383, and would later own my 70 440-6. His ammeter was doing this, and it turned out to be the welded splice. We ended up with the dash all torn apart and the harness half pulled out, he figured I'd NEVER get it back, and I wasn't too sure either!!!! I was the "hero" for awhile after that. Since that time I've been privy to maybe 10 or a dozen bad welded splices in various people's cars, some of them on here. This splice is up under the dash by the cluster, a few inches from the ammeter black wire. You simply have to pull the cluster, access the harness, and untape until you find the splice.

 

[crackedback]

Headlight on, there is likely a short somewhere in the circuit.