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Discussion Starter #1
I own a 1970 Chevelle. I started by replacing the alternator because the bearings were singing. My battery ended up dying and instead of second guessing it I just replaced it. The new battery died as well so, knowing how charging system components are prone to cascading failures, I changed the voltage regulator...battery died again. I then replaced the horn relay. Still no charging action going on. I have since replaced the fusible links and have inspected most of the wiring without finding anything obvious. I'm questioning the wiring of the horn relay because when I replaced it a red wire with a black stripe was disconnected. Can anyone give me a hint where to look next ...
 

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Have you checked to see if this is a charging problem or is the battery being drained by sitting? When the car is idling, measure the alternator large terminal with the red wire on it. It should read 13.5 volts to 14.5 volts to ground. Start there.
 

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Perhaps you bought a bad alternator?
 

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After taking some readings with the volt meter I find that when the key is on, engine not running I do NOT get 12V to the field wires on the alternator. With the engine running I only see battery voltage (12.35VDC and then up to 12.68VDC @ 1000RPM) from the large red wire on the back of the alternator. I had an experience last night that really got me scratching my head. I pulled into a gas station and when I tried to restart the car it acted like the battery was dead. My son-in-law attempted a jump start with no success. I took the battery home and checked the voltage and got 12.3VDC. I then put the battery on the charger and it was only drawing 1A. On one hand it seems that the alterator is bad, although on the other hand it seems as though I'm dealing with a direct short which could explain the low voltage readings from the alternator. At this point I'm thinking that I may have multiple problems.
 

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"After taking some readings with the volt meter I find that when the key is on, engine not running I do NOT get 12V to the field wires on the alternator."

There's only 1 field wire and when the engine is not running you will not see 12 volts on it.

"With the engine running I only see battery voltage (12.35VDC and then up to 12.68VDC @ 1000RPM) from the large red wire on the back of the alternator."

You are not getting an output out of the alternator. Maybe you do have 2 problems but chase them one at a time. Try these steps and post back the results.

1, Remove the plug from the regulator.
2, Turn the ignition key to the ON position.
3, Measure the regulator connector brown wire to a good ground. You should have around 12 volts.
4, If (3) is around 12 volts, switch the key to OFF.
5, Install the regulator connector.
6, Remove the plug from the alternator.
7, Turn the ignition key to the ON position.
8, Measure the alternator connector blue wire to a good ground. You should have around 12 volts.
9, If (8) is around 12 volts, switch the key to OFF.
10, Install the alternator connector and start the engine.
11, Again measure the alternator connector blue wire to a good ground. You should have around 12+ volts.
Post back the results.
 

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Discussion Starter #6
With regulator connector unplugged and key ON brown wire reads 11.98VDC.

With regulator connector reattached, alternator plug removed and key ON blue wire on alternator plug reads 9.66VDC.

With alternator connector reattached, engine started blue wire reads 3.15VDC.
 

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"With regulator connector unplugged and key ON brown wire reads 11.98VDC."

That's fine. Means the ignition switch and the wiring to the regulator is OK.

"With regulator connector reattached, alternator plug removed and key ON blue wire on alternator plug reads 9.66VDC."

Problem here. The regulator should not be dropping the voltage 2.5 volts. The regulator ties the blue and brown wires together. The 12 volts (11.98) should be seen on the blue wire. Regulator case grounded?, either with a ground strap or through one of its feet? Bad connection on one side of the blue wire? Its very hard to measure the blue wire coming out of the regulator because of the way it is mounted. You might have to unscrew the regulator to try this but keep the regulator grounded when you take the measurement.

"With alternator connector reattached, engine started blue wire reads 3.15VDC."

Alternator is not starting probably due to the low voltage out of the regulator. With everything plugged in, engine idling, you might want to flash the alternator. Touch a piece of wire from the blue wire to the large red wire on the rear terminal. Do this for a couple of seconds. The alternator red wire should then go to 14.00 volts or so. Shows 2 things. The alternator itself is OK. Problem is still back at the regulator with its low voltage.
 

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Discussion Starter #9
Thanks Peter F. I read your post.

I believe that we're zeroing in on this. When I flashed the field on the alterator it definately started. I read 17.15VDC from the alterator while I was holding a jumper from the blue wire over to the big red wire on the back of the alternator. As soon as I removed the jumper it went back down to 12.26VDC.

I then checked the ground on the regulator case by checking for continuity between the case and the negative battery pole. It seemed good. I replaced and shined up the chassis ground strap anyway to be sure I still read 9.97VDC on the blue wire while key was on (engine off).

I replaced the regulator with a known good one and got the same result. Swapped them back. What else could be pulling this down?
 

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Problem still points back to the regulator or it's wiring. Flashing the alternator allowed it to come on. Still concerned why that blue wire was 2.5 volts low when the connector was pulled from the alternator.
Maybe a poor or bad crimp joint on one end of the blue wire. Try flashing the alternator a different way.
Leave the alternator connector plugged in.
Unplug the regulator connector.
Start engine
On the regulator connector jumper F to 3 for a second or two.
Alternator should again go high on the B+ red wire.
 

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Discussion Starter #11
Tried what you said and it did start the alternator. I also tested resistance of the blue wire from regulator connector to the alternator connector and got zero ohms.

Allow me to share another symptom with you. With a fresh charged battery I drive about 5 miles and shut the engine off. The engine will not restart although the battery is still reading strong. If I let the car cool down the engine will start. My brother (airline mechanic) suggested that the starter solenoid is shorted. He thought that it is probably responsible for pulling the current down and at higher temperature (due to proximity to the exhaust) is preventing the car from starting. In your experience does this sound reasonable?
 

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Still looks like a regulator problem. Just a couple of things to double check before changing it.

Check to make sure there is continuity on the relay wire (white) from the alternator connector to the regulator connector. Suspect there is but best to check.

You do have a ground wire from battery (-) to the right inside fender? Guessing it's there but just checking.

At this point I would install another regulator. Try a solid state unit. Places like Autozone sell the Wells VR715 solid state regulator for around $11.00. Disconnect the battery before installing. Solid state units don't like to be plugged in with a "hot" connector. Be sure its case is grounded.

Starting problem could be:
Dirty connections at the battery
Poor or bad ground connection at the block
Poor battery cables
Cracked or worn solenoid
If it was me I'd start eliminating things in that order.
 

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Discussion Starter #13
I changed the regulator out last night with a known good one and got no difference with my voltage readings. I will do a more comprehensive test of my wires and connectors today...
 

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I agree with John. When the engine is off the blue wire (reg F term) must read the same as the brown wire (reg #4 term). The regulator connects these together with a set of contacts when the engine isn't running.

What do the regulator wires do as I described in the key on engine off and key on engine running tests in that other post? List the voltages you get for these tests.

These are the tests;
KOEO = key on engine off and KOER = key on engine running.
F terminal - KOEO = #4, some voltage KOER = 9-12V typically
#2 terminal - KOEO = 0V KOER = >3.2V
#3 terminal - KOEO = 12V KOER = 12V
#4 terminal - KOEO = F, some voltage KOER = 12V

Peter
 

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I may have misspoke (typed :confused: ) You checked the brown wire with the regulator disconnected and the blue with it connected. That will not produce the same result. Check both with it connected and post back (and include the other tests - I can't really be any further help without them).

FYI John. On the regulator I checked there is about 26 ohms from term #4 to ground. This 26 ohms will create a voltage divider with the resistance of the bulb and the bulb bypass resistor. This divider will not allow full battery voltage on the brown or blue wire with just the alternator unplugged.

Peter
 

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You may be right Peter. I'll check into it. Offhand I don't see its purpose.
*Thinking Out loud*
Maybe I'm missing the obvious again. When you apply the excitation voltage to the field, the alternator should go high, which it does. Once the alternator starts producing, a voltage is outputed from the blue wire to turn off the idiot light. The alternator should not shut off once the jumper is removed from the blue field wire. It should remain high. This alternator keeps shutting down and only works if it is flashed.
Think I would pull it and have it load tested at the auto store.
 

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Actually John, the blue wire, through the charging light current, provides a little field current to the alternator. The White wire then begins producing a voltage and feeds it back to the regulator. This voltage energizes a contact which connects the battery voltage at terminal 3 to the light connected at terminal 4. Since the light has battery voltage on both sides it does not light.

I'm really thinking the problem is in the white wire feedback signal. If this voltage does not go to about 3.5 or so when first started the regulator does not kick in.

Peter
 

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With all this thinking going on you would think we could see the answer. You concur that the alternator should remain high once it has started? Still appears that it's shutting down. I'm going to go with a bench test on the alternator. Even if the first guy says it's good, I'd have it rechecked somewhere else.
 

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To me, it's looking like it's either the alternator or the white control wire.

I still want to see the results of the voltage checks I listed.

Peter
 

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hmmmm, I've been patiently keeping my mouth closed on this...
 
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