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1967 Mustang Charging System Questions

We just got a 67 mustang with 302 and after driving it for about 2 weeks it quit on way home and wouldnt restart. Recharged the battery and it started right up and drive for another 2 days and then it quit again, in the rain. Towed it home charged the battery, removed alternator and took it apart and found some chiped brushes, but couldnt test it further, so got a new one. Not 100% sure the wiring is back on correctly. Got wiring diagram at library yesterday and did some diagnostic tests.

Test results

  1. engine off battery voltage 12.44v
  2. ignition switch off 0.23v between alt regulator S and gnd
  3. ignition switch on 12.34v between alt reg S and gnd - conclusion alt reg S to gnd is ok (car will start also)
  4. Car off 5.87V from alt reg A to F terminals
  5. car on at idle 0.97v (and 0.89v 2nd time) from alt reg A to F terminals
  6. Car at idle alternator white wire (field?) to battery - or gnd
11.18v

What is bothering me is tests 4 and 5 above. I am not sure what they should read but it seems to me that it should be 12V or above when the motor/alt are running.

From reading this fourm it seems like there are some other tests to perform this afternoon.

  1. voltage on battery at idle sb 13.8 to 15v
  2. voltage on battery at 2000 rmp 14.5 to 15.4v
  3. check ground strap from engine to firewall
  4. ground wire from alternator to engine
  5. alt belt tightness

Any other suggestions to determine if the alternator is wired correctly, system is charging the battery, other problems, so I dont get stranded in the rain again.

Thanks.

Reply to
mpate
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Update on some of these tests.

  1. battery voltage with car off 12.7v
  2. battery voltage at idle 12.36v
  3. battery voltage at ~2000 rpm 12.39v
  4. battery voltage with car off again 12.54v
  5. ground wire from firewall to engine - attached to firewall on passenger side of firewall, NOT attached to engine
  6. ground wire from alt to engine in place and attached to dip stick bolt
  7. alt belt is tight

So with this new test info it seems like there are a few things left. A. put the ground wire from the firewall to the engine back on - anybody know where this would bolt onto the engine? I have been feeling around the back of the head on the passenger side but can only feel a large hole and it dosent fit the bolt. Where is this strap supposed to be attached on a 302? B. maybe the alternator regulator is not working between the A and F pins - which is the field wire from the alternator or white wire and the A pin which is the yellow wire going to the starter motor relay - it is not working because of the ground strap between the firewall and the engine is disconnected or because the regulator between the A&F pins is blown. C. Not sure what else it could be - any experience here?

Thanks.

Reply to
mpate

One more update. We hooked the ground strap from the firewall to the engine back up; we verified it has continuity with the dvm. Engine off 12.7v on the battery Engine on at idle 12.3V on battery

What else to check?

My conclusion is that the alternator regulator between A and F is dead. I am still bothered by the earlier voltage checks across A & F with the engine on and off; I guess I should repeat this with the ground strap reconnected and see if it is the same.

Reply to
mpate

Try tapping the reg. with a screwdriver handle during idle, can you hear the alt. pulling the motor down?

Reply to
GILL

After reading your voltage test results, I question your methods. What are you using to get these readings?

With the engine running about 2,000 RPM you should have about 13.6 volts +/- a bit on the battery terminals. If you don't, the alternator is not working. You can disconnect the regulator and jump the "A" to the "F" terminal on the regulator connector. This should turn the alternator on full blast and the battery voltage should jump up to 15. Don't take too long to do this as it's not good for the battery and any accessories that happen to be on. That will test the alternator. If it's working the problem is wiring or the regulator.

Al

Reply to
Big Al

Gil & Al:

I tried tapping on the alternator regulator today while it was at idel and it shut the engine off. We started it again and check the voltage of the battery while the engine was at idle and the voltage was 12.3v, when the engine was off it was 12.7v - checked with a volt meter across the + and - of the battery terminals. We started it again and got the rpm up to maybe 1500 and tapped the alt regulator again and it shut the car off again.

So off we went to get a new alt regulator and put it in and did the voltage test on the battery running and stopped with about the same voltages 12.3 and 12.7v.

I am now wondering if the alternator is actually charging all the time or only when some condition triggers it to run and charge the battery in this 1967 mustang. So is the alternator charging all the time? If not, what condition or mechanism triggers the alternator to charge and put the load on the engine?

We have also double checked the wires on the back of the alternator and buzzed them out for continuity.

What else could it be, that causes us to get the lower voltage across the battery when the car is on?

Thanks.

Reply to
mpate

If you pull the positive cable off the battery while the car is running and it dies, you can be pretty sure it's the alternator. The older regulators had mechanical points inside them that when signaled would close and make the alt. charge the battery. Sometimes the points would stick open and it's why I mentioned the tapping. Make sure you have all your + & - lined up. :)

Reply to
GILL

To answer the question, when the engine is running the alternator should be charging. What are you using to measure the voltage?

Al

Reply to
Big Al

Reply to
mark james

...the best thing I ever did was get rid of

Go ONE WIRE! Mpate.. please do what mark said. Especially if it's a 'frequent driver'. I been working on cars since they used generators, and believe me.. the one wire is the way to go. Do research on the net to see how to hook it up to see charge state. Otherwise, you shouldnt be having to do more than trace wires and replace parts. Voltage readings anywhere but the A terminal are confusing and dont really mean much because of that, too many variables Problem is that the VR was a precision electro-mechanical instrument and the 'art' of making them has been lost.

Otherwise go to the library and to google and read up, learn such fascinating stuff as 'flashing the field'... which IF YOURE SURE your wiring is intact may be what's needed. Until the next time..

You can always leave the original wiring intact and nicely tucked up.

Reply to
Backyard Mechanic

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