[6T9GTO]

My 69 GTO is not charging. I took the battery out yesterday for some maintenance and replaced it. Now when I turn on the key, the GEN light has very slight glow. When cranking, it lights up bright. When running, it has the same very slight glow to it. I can remove the battery NEG cable and the motor shuts off.

Should I try a new regulator? The one on there looks pretty new, but I don't remeber when I put it on.

Any advice is appreciated.

-Bill

[Ben M.]

What is the voltage put out by the alternator?

[6T9GTO]

I haven't checked it yet.

[6T9GTO]

Update: Took alternator to Advance Auto Parts. It checked ou OK. I bought one of their voltage regulators. It didn't have any of the resistors ,or whatever they are called, on the back. Hooked it up and same deal, but it will put out the GEN light when you rev it up. Unhooked the neg cable while running, and the engine died.

Should I try a "better" voltage regulator?

[george kujanski]

You need to diagnose the problem, not keep replacing parts.

Get a voltmeter/multimeter and measure the battery voltage when off, when engine running, engine running with lights on, etc. And get back to us with the results.

George

[Schurkey]

Originally Posted by 6T9GTO

I can remove the battery NEG cable and the motor shuts off.

Should I try a new regulator? The one on there looks pretty new, but I don't remeber when I put it on.

Disconnecting the battery with the engine running is an EXCELLENT way to fry the diodes in the alternator. Disconnecting the cable creates a momentary voltage surge way above what the diodes are comfortable with.

DO NOT "try" a new regulator. Test first, replace parts second.

1. What is battery voltage with everything shut off. This is called "Open-Circuit" Voltage (OCV)--and it better be 12.6--12.7 or so. If low, charge battery.

2. What is charging voltage at the ALTERNATOR output terminal, fast-idle (1200--1700 rpm) Should be 13.5--15 volts. 14.2--14.5 preferred.

3. What is charging voltage at the BATTERY + terminal--same idle speed? Better be VERY close to voltage at the alternator. If not, wire harness has problems.

4. Engine off, disconnect 4-wire connector at regulator. Install jumper between #3 and "F" (#1) on the CONNECTOR, not the regulator itself. Start engine, check charging voltage. Should be 16+ volts, alternator will whine. Don't run engine more than needed to check voltage, alternator will get HOT. This is called "Full-Fielding" the alternator. The alternator will produce it's MAXIMUM power at that RPM.

If it doesn't charge when full-fielded, you've got a defective alternator or a defective wire harness. Check continuity from "F" at the harness connector to the wire of the same color at the two-wire plug on the alternator. Check continuity of the other wire in the two-wire plug on the alternator to #2 on the connector at the regulator.

If it charges when full-fielded, and didn't before--regulator is defective.




I STRONGLY suggest that if you find a defective alternator or defective regulator, that you install a newer 10- or 12-SI internally-regulated alternator instead. They put out way more power at idle and low engine speed than the older alternators; and they're inexpensive. You will need an alternator pigtail (about $6, maybe less) and two home-made jumper wires about three inches long.

I would not spend ten dollars to fix an old external-regulator charging system with original-style parts when the upgrade is so simple and cost-effective.

[george kujanski]

Good job, Schurkey.

George

[6T9GTO]

FIXED!!

The blue wire in the forward harness was broke. Soldered together and heat shrink - all is good now. Thanks all for your replies.

[gtofreek]

Excellent post Schurkey. Well said!

The only thing I would add to an excellent post is I always test the wires at the regulator plug and alternator with a test light. The regulator plug when unplugged should have two hot wires with the key on. They will be right next to each other and the one on the end of the plug, should be the one getting hot from the key[alt/gen light], the second one in should be hot all the time. I double check the wires at the alternator if it still does not charge when full fielding. And of course, that the battery wire at the alternator is hot when the engine is off.

[Ben M.]

Originally Posted by gtofreek

The only thing I would add to an excellent post is I always test the wires at the regulator plug and alternator with a test light.

Personally I would not use a test light for anything except "indication of some voltage." A proper multimeter will be a MUCH better diagnostic tool than a simple light.

[gtofreek]

Originally Posted by Ben M.

Personally I would not use a test light for anything except "indication of some voltage." A proper multimeter will be a MUCH better diagnostic tool than a simple light.

Meters are good for some things but a test light can tell you a lot very quickly. They both have their place.

[gtofreek]

Plus, if you know what your doing with a 12 volt test light, you can pretty much diagnose the entire starting and charging system with one very fast. Way easier and faster than a multimeter. We used a VAT 40 for the voltmeter and ammeter to see what stuff was doing, but when it came to diagnosing the problems, 99% of the time it was done in seconds with a test light. We didn't guess and swap parts either. We diagnosed right down to the actual bad part.

So to say a test light shouldn't be used is just ridiculous.

[Ben M.]

Originally Posted by gtofreek

So to say a test light shouldn't be used is just ridiculous.

I have never seen a use for them in business or the hobby world (they are actually disallowed at work). A multimeter does everything and more. If it was all I had, sure I would use it. But I wouldn't go out to get one before a multimeter.

[Schurkey]

You should see the things I've seen diagnosed with licking two fingers and touching the equipment...

Nothing wrong with using a test light in certain applications. It's very fast, but doesn't give precise voltage readings--you have to periodically calibrate your eyes to the brightness of the light.

It's like the difference between a micrometer and a go/no-go feeler guage.