TR2/3/3A Generator Warning Light on with the Alternator Charging the Battery

[mastaphixa]

The subject of this post is a 1960 Triumph TR3A that has been converted to a motorcraft type alternator with an external regulator. It has been operating normally for years. Recently the red generator light illuminates with the engine running. With the ignition on/engine off the light is on dimly and after engine start the light comes on bright. The ammeter shows a positive charge and that is confirmed with a volt meter. With the engine off battery voltage is 12v and change. After engine start a voltage of 13-14v is displayed. I have had the alternator checked and it is operating normally. I have a back up voltage regulator and have swapped it out with no change. When I swapped the regulator I noticed the removed regulator (l'll call that regulator #1) had lots of corrosion on the terminals. I installed the spare (regulator #2) and the car was back to normal. I removed the corrosion from the terminals of regulator #1 and reinstalled it and the car was back to normal. Thinking I had fixed the problem I enjoyed a beverage and patted myself on the back. The next day I started the car and I was back to square one with the light on again! While the engine is running I can hear the belt make a little noise which goes away if I disconnect the wire from the I terminal of the regulator and the generator light is off at that point. I must admit I am a bit confused at this point. I have checked the battery with a load cell and it is healthy.
Any help would be appreciated.

 

[bobhustead]

If you have the thin belt as a result of the alternator conversion, check for tightness. The squeak indicates this possibility. What is your idle and is it always the same.
Bob

 

[mastaphixa]

Bob,
Thanks for the reply. It is still a wide belt and it is appropriately slack. When I pull the I terminal wire off the regulator the generator light goes out and there is an increase in the idle speed. Just back from a test drive. Generator light on, Ammeter in the +, Volts are reading 13.8-14.4., about 10 miles the Generator light went out, Ammeter in the +, Voltmeter reads 13.5-13.8. When I shut the engine down and then turned the key to the on position there is now no generator light at all. The Alternator is still charging but the voltage difference between engine off/key off and engine running is not nearly as great with just about 1 volt above battery voltage while engine running. I have a battery switch on the negative terminal which I opened while the engine was running and it never skipped a beat. I pulled the I lead off the regulator and the idle speed increased as there was no longer a load from the alternator. Still no generator light on with the engine off/key on. I'm stumped.

 

[Sarastro]

With a generator, the lamp is connected between the battery's (+) voltage and the generator output. That way, when the generator is not running, with zero output voltage, there is 12V across the lamp and it goes on. When the generator starts operating, its voltage is equal to the system voltage, so there is no voltage across the lamp and it goes out.

With alternators, it's a little different. Most modern alternators have an internal regulator, with an electronic switch for the lamp. The lamp does not depend directly on the alternator's output. So, if the part of the regulator circuit responsible for the lamp fails, the lamp will go off (or maybe will be stuck on) independent of the function of the alternator and its regulator.

I'm not familiar with your alternator, but if it has an external regulator, it's probably an older design. Probably it works the same way as more modern ones, though. At first, it sounds to me like a bad regulator. But since both units showed the same problem, a bad wire or connector someplace, or a bad ground, also seems likely.

 

[mastaphixa]

Sarastro, thanks for your post. In my previous post I noted the generator light was out all the time. I swapped out regulators again and I am back where I started with a generator light on dim when the key is on and the engine off and a generator light on bright when the key is on engine running. The alternator is still putting out a charge. I have accessed the generator light bulb holder in the panel and can see the yellow wire attached to one side and the lead from the ignition switch attached to the other. There is a shunt resistor across the terminals. I'm going to investigate that part of the circuit further.