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Discussion Starter · #1 ·
hey

i have run into a very frustrating electrical problem and after going through all the related previous posts i have exhausted my possible solutions. Help! Here's the story: was about to leave for a cross country trip when the GEN light comes on. I bring the car home and check it out. I have an autometer voltmeter under the dash hooked up to key-on accesory voltage. As the car idles, it shows only twelve. Normally I get almost 14. As I increase engine RPM in neutral the voltage increases up to the meters limit of 16. I had the alternator tested at pepboys. It works. No change. I tried a new alternator. No change either. Tried replacing the external voltage regulator. No change. Checked grounds, checked for voltage drops between alt and bat. With the voltage regulator disconnected the GEN light finally goes off. However, lights are dim and as i rev the engine the volts don't go up anymore.. it stays at twelve. Any ideas?

Dan
 

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I had the same problem on a 69 El Camino. Never figured out the problem before i swapped to a one wire alt. Anyone know, im curious too.
 

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Discussion Starter · #3 ·
thats what its coming to at this point. This is my daily driver and i need to get on the road. What is the simplest direct bolt in.. i went through tech ref 14 briefly but I don't have the time to construct custom brackets and the like.

I have read and seen the GM 78amp 12SI mentioned.. will this fit? Or should I get another regulator?
 

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The GM internal regulator alternators S/B a drop in fit. The case is the same. If you don't want to do any harness modifications there are harness kits available. One side coverts the alternator side wiring with a pigtail connector. Another piece modified the external regulator connector. The kit makes the job simple. Believe the sponsor sells them.
 

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Discussion Starter · #5 ·
any idea as to what may have happened? its strange.. it seems as if the voltage isn't being "regulated". The alt gets spun faster, it generates more power without constraint. When I disconnect the VR, voltage is static..
 

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If I read things right, sounds like your new alternator isn't putting out. Only getting a constant 12 volts. Normally I don't disconnect the regulator with the engine running. But since you did, and the idiot light goes on and off sounds like the blue field wire from the alternator to the regulator is ok.
Couple of thoughts.
Without disconnecting anything measure the R (white) wire, with a meter, to frame ground. Engine running at idle and measuring it at the regulator it should be around 7-8 volts. This, at least, checks that there isn't a problem with this.
Since you changed the alternator and keep pulling the regulator, the new alternator may have to be flashed. The field or coil needs voltage to get it started. Using a jumper wire, jump the battery positive to the F wire (blue) on the alternator. Do this for only a second or two.
 

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If the alt and reg are known good then the problem is in the wiring. Some things to check. Check the orange Fusible link connected to terminal #3 of the regulator. Unplug the regulator and the two wire connector at the alternator, use an ohmmeter to check the white wire from the reg connection to the alt connection. Make sure the regulator is grounded. Take a good look at all connections to the regulator and alternator.
 

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The first regulator I bought was junk. Just keep that in mind.

Disconnect the regulator. Jump between the F(1) and 3 terminal at the regulator and the alternator should go full on. It should easily make 16 or 17 volts when you rev the car. It's a good idea to have the lights on during this test and not rev the motor (ie, warm it up before testing so it'll start at and idle).

Check the light wiring by grounding terminal 4. It should go on when grounded and off when not.

Terminal 2 should have at least 3.5V as soon as the car is started to energize the regulator.

On the regulator the connections are as follows;

Terminal F(1) goes to the field wire on the alternator. Putting voltage on the field makes the alternator work.

Terminal 2 goes to the alternator R terminal provides the voltage to close the field contact in the regulator and start it working.

Terminal 3 is just battery voltage. It's used to provide the power for the field and is connected to terminal 4 and the voltage regulating coil once terminal 2 goes > 3.5V.

Terminal 4 connects to the light. The light has power on the other side and the light current goes through the field and makes the alternator work enough to get terminal 2 > 3.5V when started. The light is paralleled by a resistor so the current is there even if the light burns out.

I hope this helps.

Peter
 

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Discussion Starter · #9 ·
thank you all for the replies.. i would have liked to track down the problem but had to get on the road and just now got my internet up to reply. I ended up tearing out both the alternator and VR and upgrading to an internally regulated unit.. crude but effective and now i gots mo ampz.

Dan
'72
 
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