Please help! I am running out of ideas on what to do to fix my charging system in my 1972 1.7L.

Two weeks ago it refused to start. Got it started a couple of times by pushing.

Took it to a NAPA store, had them test the battery, they said it was bad. Took it to an Interstate Battery store, they tested the battery good, but said the charging voltage was low (around 12.8-12.9). Got it back home, measured the voltage at the battery, it was 13.4. Tried replacing the voltage regulator with a known good one, same exact results.

Then I thought maybe my battery was indeed bad. Couple of days ago bought a brand new Optima, and put it in today. Measured the voltage at the battery with engine running to 2000rpm, got 13.8, thought all was good.

Went for a drive around. One strange thing I noticed, there was a sound like a relay clicking on and off, on and off, like a blinker, but with a slower frequency. Went on like that for at least 10 minutes while driving. Sound was coming from under the panel, left side, where the fuses are. Thought that maybe this had something to do with the charging, but when I stopped after half an hour at a gas station, voltage measured 13.8, even with the headlights on, and the clicking had stopped. Thought I am out of the woods.

Got home, checked again the voltage, 12.2-12.3 no matter what the engine RPM. So basically not charging at all. No more clicking.

The red light in the panel comes on when the engine is not working but the key is on. Otherwise the light is off, even when the alternator is clearly not charging.

Any suggestions on what to test? What should the resistances be between the three electrodes in the plug for the voltage regulator? I suspect something is messed up with that wiring, but can't figure out what. (The system worked fine until two weeks ago, and moreover the car has not been cannibalized in any way.) Or could it be a fuse that is making a bad contact?

Thanks!

Hopefully Superhawk996 will chime in.
He's the best on troubleshooting this kind of stuff.

Do you have clamp on amp-meter? It is possible to have an alternator output what looks to be the proper voltage and no current. It has been a few decades since I tested an external regulator. As I remember if you have the regulator sending 12 volts to the field coil on the alternator, it is working. You should be able to send 12 volts to the field coil with a test light to see if the voltage increases. just don't do it very long. If when the car is running and the voltage is lower than when it is off and goes up when you apply voltage to the field terminal. It is likely a regulator. This is where the current clamp helps. Find the 10 gauge from the alternator to the battery clamp around that wire. There should be a arrow on the side of the clamp to indicate current flow. Make sure you have it set to DC current. When the car is running your should see the current flow from the alternator to the battery. You can increase the load by turning on the lights. If you see negative amps or very little the alternator is not charging. You can apply 12volts the field if you see current it is the regulator. Don't do it for very long you could overcharge.
I think Autozone will test it for you if you have one near you.

Thank you for the kind words. I'm not nearly that goood. 4 years as an electronics tech for USAF helps a bit.

Sounds a lot like symptoms of a faulty voltage regulator. The older mechanical style can be more prone to intermitent sticking and could align to the symptoms described.

The fact that you head a cycling clicking noise in the vicinity of the relay board sounds to me like the regulator was cycling between the charge / no-charge cylcle in an attempt to regulate voltage. It's odd that you could hear it. It usually isn't clicking that loud.

You could also have a failing alternator which is sourcing current intermittently. There are diodes in there that could be overheating and failing when they are hot.

I argree with @914e post recommending use of the current clamp. Current flow is the definative way to tell if the battery is charging. Current into the battery = charging. Monitoring current flow in conjuction with alternator output voltage will tell you what's going on.

Perhaps this will help?

***Analogy ON***
Think of a battery as a water tower, it is 12 feet above the ground.
To get water into it, you need to lift the water above the rim of the tower which is 13.6 feet.
When you use the water you are draining the tower.
If the Pump is working, you are never using the water in the tower, just the water from the pump.
***Analogy OFF***

The system in the car IS that simple. Your problem is simple as well.

A few rules:
Lead Acid Batteries are brutally simple - the chemistry is simple
Lead Acid Batteries take usage (cycles) or abuse (hooked up BlacktoRed) to 'go bad'
If the battery is 'NEW' it can almost always be resurrected
if it is run down all of the way (it will then test bad using a VOM) and some chargers will not charge it.
Batteries, in the old days, were tested by measuring the strength of the acid, all batteries are now sealed (too dangerous) so they are 'tested' with meters that kinda tell part of the story - BUT - can also tell you to buy a new one when the acid is fine and the lead is still OK, just needs a charge

YOUR CAR

PRIOR TO DOING ANYTHING IN THIS OR ANY OTHER POSTING, TAKE OFF YOUR WATCH, RINGS OR BRACELETS (Med ID, etc.)

So you either have a Goes-Inta OR a Goes-Outa problem. Either not enough is current is available to operate the car or there is a permanent leak that is removing energy from your battery while you are not looking.

The magic number is 13.6*
Hook your voltmeter to the battery with the car NOT running. It should be 12V. If it is +/- 10% of 12 volts, no problem.

Start the car.

Turn on the lights

Watch the voltmeter, if the alternator is good, it will say 13.6* (off perhaps by the same % as when you measured the battery PRIOR to starting the car - meter error)

If the voltage drops occasionally then there is an intermittent problem with the voltage regulator - replace it.
..........for the purists and EE types - yes this could also be the alternator - the Voltage Regulator is easy and cheap to replace, we start there.........

If the voltage is weak 9, 10 or 11v, the Alternator may not be able to take the load of the car. Try turning off the lights, if the voltage comes up a bit (while the car is running) the Alternator is suspect. The alternator cannot push up to 13.6 since the car is pulling the current (water) out of the battery (tower) faster than the Alternator can push out current (water).


Major Concept
While you are running your car, you are never really using the battery. The alternator SHOULD be supplying a voltage above the batteries voltage: remember it is 13.6. When the car is running the alternator will supply enough current to run the car, accessories and charge the battery if the battery is not fully charged.


Things to do prior to looking at the Alternator or the Voltage Regulator.

GROUND - we went through this last week with someone from England. 914s are notorious for having grounding problems. Take a jumper cable and jump the battery to the chassis (other than the ground bolt) or to the engine. HOWEVER, if you can start the car, and it runs correctly grounding is most likely not a problem.

CURRENT LEAK - this is a major culprit of current theft. There are a few always HOT wires running throughout the 914 wiring harness, sometimes the PO or perhaps you have added an accessory that should only be on while the car is running BUT has been connected to the battery.. To check this do the following.

1. Turn the car off, take off the Negative (-) wire from the battery
2. Put your meter in AMP mode (if you do not have an amp meter, get a cheap one)
3. Connect one cable from the AMP meter to the negative terminal of the battery AND the other cable from the AMP meter to the Chassis.
4. The meter should say 0 or the equivalent of "NO" current.
5. If the meter is registering something (anything) there is a current leak
6. Remove a fuse (one at a time) from the fuse box in the cabin of the car until the amp meter goes to Zero.
7. If the amp meter never goes to zero, you have a bigger problem. PM ME.



* Why do we use the charging voltage of 13.6?????

The details are involved and have to do with Peurkerts Law and the physics of Electrolytic Chemistry, however in short:

"Consider a battery that has been completely discharged (such as occurs when leaving the car lights on overnight, a current draw of about 6 amps). If it then is given a fast charge for only a few minutes, the battery plates charge only near the interface between the plates and the electrolyte. In this case the battery voltage might rise to a value near that of the charger voltage; this causes the charging current to decrease significantly. After a few hours this interface charge will spread to the volume of the electrode and electrolyte; this leads to an interface charge so low that it may be insufficient to start the car.[26] As long as the charging voltage stays below the gassing voltage (about 14.4 volts in a normal lead–acid battery), battery damage is unlikely, and in time the battery should return to a nominally charged state." https://en.wikipedia.org/wiki/Lead%E2%80%93acid_battery