Diagnosing charging system, external regulator - Chevelle Tech
Electrical & Wiring Troubleshooting electrical problems.

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post #1 of 6 (permalink) Old Jan 10th, 09, 8:25 AM Thread Starter
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Diagnosing charging system, external regulator

This is on '67 with external regulator. Battery stays on Tender, so it's hot. Shows 13.1 at battery & about same at red wire on back of alternator with nothing switched on. When running shows same voltage at red wire on alternator. Guage on dash shows discharge when using any accessory with car running. Someone told me that external regulator only tells alternator what to do, and I should still be showing from 13 to 14 on red wire when cranked. Alternator and regulator done by THE guru, and car has new underhood harness.

I started to unhook red wire from back of alternator and see if those readings tell me anything, but don't want to risk popping something electrical.
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post #2 of 6 (permalink) Old Jan 10th, 09, 12:44 PM
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Re: Diagnosing charging system, external regulator

The red wire on the back of the alt is tied directly to the battery, through the main harness splice then junction block. It should read exactly the same as battery when car is off. When running with accessories on it should read around 15V, trying to keep the battery charged. Sounds like your system is not charging. So it's wiring, voltage reg, or alt.

Number 3 wire on the voltage reg also goes to the main splice. This wire is used to sense voltage and tell the regulator what it needs to do. Here is post that describes the wiring and how to test your voltage regulator. Since it's a new harness I would verify that first.

voltage regulator wiring


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post #3 of 6 (permalink) Old Jan 10th, 09, 4:36 PM
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Re: Diagnosing charging system, external regulator

If this were in MY garage, I'd unhook the four-wire connector at the external voltage regulator, start the engine--run it at fast idle, and then put a jumper wire between the F terminal and the #3 terminal.

The alternator better throw LOTS of volts; and put out near it's rated amperage.

Don't keep the jumper wire connected very long--you can overheat the alternator.

IF the alternator doesn't "put out", you need to check for voltage at the F (usually blue) wire AT THE ALTERNATOR. There should be continuity between the F wire at the regulator, and at the alternator.

'Course, if it was in MY garage, I'd pitch the external-regulated alternator in favor of an internal-regulated unit--probably a 12SI.
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post #4 of 6 (permalink) Old Jan 10th, 09, 5:51 PM
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Re: Diagnosing charging system, external regulator

If the alternator is producing properly 13-14 volts and then you are getting the same reading at the battery, it sounds good. But a good number rule of thumb, charge volts at the battery when not raising rpms shuould be 12.8-13 so you are right in the box. When sitting a battery should read about 12.8ish or so like a said before.

The regulator does just that regulate the voltage that is put out by the alternator. If you get too much voltage, then you will start getting burned wires, and blown bulbs, in headlights,fuses,lamps, etc.... I would try repalcing the voltage regulator first and see if it makes a difference. Also beware because with our cars if I remember correctly, the 14.4 volts reading will not be at the voltage regulator but at the splice located by the Horn relay.

What ever you do, do not disconnect the negative cable on the battery to see if the car will still run to test the alternator. This is a common myth and method that can damage your alternator and charging system. While the car is off, try disconnecting the negative cable on the battery then take the cable at tap the negative terminal, if you get a spark or play, then something is still on or you have a ground issue somewhere and thats a whole topic in itself.

Chevy Muscle cars can be misleading with voltage readings due to the nature of the long wiring and the shear power of these performance engines. But the ranges should be standard 12.5-12.8-13ish at the battery when not raising the rpms. If you have a drop in voltage in your gauge when you turn accessories on, sounds like the voltage regulator, check the wiring, pig tail connections, etc...

I had to replace my wiring pigtail from the alternator and the pigtail to the voltage regulator to the splice and put better wiring and connector. AND STAY OEM so you can look at the diagram, Do not rig it up, I repeat, it will only be a temp fix.

Good Luck!
Read this Bro: http://www.madelectrical.com/electri...evymain1.shtml

Last edited by shonuff; Jan 10th, 09 at 5:53 PM. Reason: ****
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post #5 of 6 (permalink) Old Jan 10th, 09, 6:01 PM
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Re: Diagnosing charging system, external regulator

A 12SI is a good upgrade but some guys want to stay original. I still have an external regulator and haven't had any problems with it. Yes the headlights dim some at night at idle but I don't drive it that much in the dark. It doesn't get dark here until after 10 PM in the summer and in the winter, well it mostly stays in the garage. But I do agree if you want nice bright lights or have added accessories an upgrade is in order. Also the link I provided does have a test to verify the alt can put out the required voltage. Being a new wiring harness was installed I suspect that may be the problem, who knows. The link, thanks Peter F, has the tests needed to determine if it's wiring, voltage reg, or alt.

EDIT: John is correct, they call it a 12v system but in reality 14.4v is the optimum operating voltage. There is a very short wire from the voltage regulator to the main splice. This is a voltage sense wire, carries very little current, so the voltage at the regulator should be the same as at the main splice. The whole idea is to maintain the voltage at the main splice at the proper level. The link John provided has a very good write up on the design and why, as he said, you don't want to change it.


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post #6 of 6 (permalink) Old Jan 10th, 09, 7:31 PM
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Re: Diagnosing charging system, external regulator

I had a charging issue one time as well. The Generator light kept staying on and the car would not start sometimes, so we tested the Alt, the fuse box, grounds, battery, ext regulator, windsheild wiper motor, checked all the switches, etc... The voltage regulator was not functioning properly and not sending eough volts from the alt to the battery. It was the cheap a** autozone voltage regulator. I went to Oreily's popped a new one on, and 3 months later, it starts like the motor is going to jump out the hood. I use my 69 as a daily driver. I went back and made sure all my wires were solid and wrapped in electrical tape. It looks cool because you really cannot see the wires in the engine compartment.

I also replaced the pig tail at the alternator and voltage regulator.....prob about $4.99 a piece from Oreilly's. Made sure I had good connections and tried to keep they wires way from the engine as much as possible. The wires running from the alternator, I wrappd them really solid as these blocks can get pretty hot. They run right between the valve cover and intake manifold.

As far as accesories I have a Viper Alarm with 3 millions options on it, Kenwood radio etc....

As for mods.....just make sure you keep in mind that your mods will affect the basic system so if you add amps(stereo amps etc...) or tv's etc... mods will come. But mods like using a high ampage Alt 55-61amp standard to a 100-200amp alternator or an extra drycell battery. They also have a alt crossover but once again thats another convo.

Sounds like a ext voltage regulator problem. I have bought them from the store before and they were bad right off the shelf. It is like your brain for voltage or filter.
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