I've recently purchased a 71 Cuda (340 4 speed) and found myself stranded on a couple of occasions because the battery didn't have enough oompf to turn the starter over. I've charged the battery and attempted to perform a few tests. I tested the electronic voltage regulator by attaching a multi meter to the 2 blue wires on the ballast resistor and grounding the other lead and found it reads around 11.5 volts. I've also put the same multi meter on the alternator and found it to read the same. I then jumped the voltage regulator and found the discharge of the alternator did not change. Do I have a bad alternator? Are there other tests I should perform to find out what's causing the alternator to not put out enough voltage? The battery, once charged, will hold enough charge to start the car for a couple of dozen times, but then it runs out of juice. Any suggestions???
Charging problem
- Thread starter JohnK
- Start date
I haven't found it yet. I replaced the voltage regulator and alternator with no change. The voltage regulator has a grounding strap that is bolted to the block using one of the trans bolts. I also charged the battery and it holds 12.2 volts for a couple of days (without the car running) so it appears the battery is not the issue. Where should the alternator be grounded to the body/block? Should the ECU also be grounded to the body/block? The paint on the car looks pretty new, so I'm assuming that I may need a grounding strap on the ECU. Currently it's just bolted to the fire wall. Any other areas I should be looking for a grounding issue. I believe tha amp gauge is not the issue as it appears to work as it should. Looking forward to whatever help I can get to figure this out.
With the engine running, you should have 14 volts at the battery. If you have less, the battery isn't being charged by the alternator. Make sure you have a good ground from the regulator to the body. You may have to remove some paint on the back side of the regulator.
If you can confirm that you have good grounds, you may have a corroded bulkhead connector. The alternator wiring has to go through the bulkhead connector before it gets back to the battery. Pull the wires off at the bulkhead, inspect and clean the connections. Use some dialectric grease on the connections to prevent condensation from forming.
If you can confirm that you have good grounds, you may have a corroded bulkhead connector. The alternator wiring has to go through the bulkhead connector before it gets back to the battery. Pull the wires off at the bulkhead, inspect and clean the connections. Use some dialectric grease on the connections to prevent condensation from forming.
Take your multi meter and measure the resistance from the alternator stud to the battery + (with the negative post unconnected). Do the same with the two wires going from the regulator to the alternator. You should have a very low resistance of something like 0.05 ohms. If you have more than that I will result in a voltage drop from the alternator to the battery. But with only 11.5 volts when its running it is more likely some problem with the regulation of the alternator. Also try to find out if any of the wires going from regulator to alternator are grounded.
Hope it helps!
Per
Hope it helps!
Per
R/T4speedconv
Well-Known Member
Check your ballast resistor-both sides I think one is for your ignition and the other feeds the voltage regulator. Unplug all 4 wires and ohm it out.
OK, I checked the resistance between the stud on the alternator and the + battery post with the negative battery cable removed and there was no resistance (.000 ohms). I then checked the ballast resistor (with the negative cable still removed) and the reading across the resistor was .001 ohms. I then tried to check the voltage regulator (with the negative cable still removed) and couldn't get a reading. The voltage regulator has a boot on it with 2 female connectors inside it. There are a green and a blue wire going to the boot. I tried to measure from the stud on the alternator to the female connector that I think came from the green wire with no results. I then tried the other female connector with the, I think, the blue wire going to it, to the alternator stud again with no reading. How do I check the resistance to the female connectors in this boot? Should I be reading from the stud on the alternator or from one of the wire connectors? I have a green wire going into the alternator and another connection with 2 blue wires going to it. Should I have re-connected the negative battery cable before trying the voltage regulator test?
R/T4speedconv
Well-Known Member
The stud on the alt does not go to the regulator-only to the battery plus. the blue and green wires from the regulator go to the two small wires that hang off the back side of the alt (they plug in) check them .
How do I make a connection with my multi meter into the "boot" with the 2 colored wires at the voltage regulator? If I touch the side of the female connector inside the boot, will that complete the circuit at the alternator if I'm on the same wire at the alternator? Or is there some sort of tool that I don't own that I can get that will make this easier?
You should NEVER have the negative battery cable connected when you are working on your car! It is so easy to make a short somewhere that can fry your wiring and in worse case, cause a fire.
That should be the last thing to reconnect when you are ready to fire it up and start to measure voltages and other things.
Chryco Psycho
Well-Known Member
the blue 14 ga wire should have battery voltage with the key on , the regulator should also have battery voltage on the blue wire , the green wire from the alt is the controlled ground through the regulator , grounding the green wire terminal from the alt should cause the alternator to go to full charge, approx 16 v , if it doesn,t either you are not getting 13.2 v to the blue wire or the alt is faulty , I have found new alt have been faulty . if the alternator does put out 16v with the green wire grounded the regulator or the ground to the body where the regulator is attached is faulty
I checked the resistance again (with the battery negative disconnected and the boot disconnected from the voltage regulator). I found the resistance across the ballast resistor to be 1.5 ohm. I found the resistance from the green wire to the disconnected boot to be 5.1 ohm and the resistance from the blue wire to the disconnected boot to be 4.4 ohm. This seems kinda high. Is it? If so, what could cause this?
Chryco Psycho
Well-Known Member
If I am clear you tested the green wire between the alt & reg & had 5 ohms resistance ?or were you testng to ground ?
if it is resistance in the wire between the alt & reg then you have a bad piece of wire in the circuit , same with the blue wire if tested between the alt & reg , replace both wires
if it is resistance in the wire between the alt & reg then you have a bad piece of wire in the circuit , same with the blue wire if tested between the alt & reg , replace both wires
OK, I tested the wiring between the regulator and the alternator again. When I tested the first time, I did not disconnect the wiring from the alternator, but had disconnected the boot from the voltage regulator. This time, I disconnected the green wire from the alternator and inserted my probe in the plug in connection that connects to the alternator, and inserted the other probe into what appeared to be the green wire side of the boot. It showed 0.5 ohms. The blue was tested the same way and yielded the same result. I then re-installed both the blue and the green and were not able to get a reading from the screw at the back of the alternator when connected to the green side of the regulator boot. When I switched to the blue side of the regulator boot, with the probe touching the screw with the green wire to it, I got a reading of 0.5 ohms. Is it possible that the green and blue wires are connected to the wrong terminals at the back of the alternator? Would that make a difference in the ability to control the voltage from the alternator? I also reconnected the negative battery terminal, and with the key on, showed 11.5 volts at the blue and green connections, when tested to the ground screw on the back of the alternator. The battery was showing 12 volts at this time. Surely it can't be something as simple as having the green and blue connected backward on the alternator, could it?
Chryco Psycho
Well-Known Member
no , the green & blue wires do not have a correct position , it is just power in & ground out from the field & it doesn' matter which is which
Chryco Psycho
Well-Known Member
It just needs a 16 ga wire to ground the field circuit
the block , alt housing anything close is fine , don,t leave it connected for long
the block , alt housing anything close is fine , don,t leave it connected for long
OK guys, I took all the wires loose from the voltage regulator, bulkhead connectors, ballast resistor, alternator and battery and cleaned and lubed everything and re-installed. I also checked all the grounds for tightness. After I put everything back together and re-started, it now runs as it should. I'm getting 14.5 volts at the battery at idle. Thank you all so much for your suggestions, it was really quite helpful.
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