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Perennial topic: ignition light

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M

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Along with oil pressure, the most nagging "issue" I have -- and apparently other have as well -- is the iginition light coming on when at idle.

My car has been behaving itself lately, but yesterday on a long roadtrip I noticed that the ignition light came on each time I stopped for a traffic light, etc., and engine went down to idle.

My car idles at 1100 rpm, anything under that and the light comes on, anything over that and it goes off. I recently had the tachometer rebuilt, so I think the reading is accurate (although probably set a bit high).

Some have written that their cars idle at 800-900 rpm and the light doesn't come on until it falls below that.

Next week I am scheduled to take the car into the shop for a spring (hopeful) tune-up and I will mention this to the shop guys. Randall at one time suggested that perhaps the cut-out needs to be adjusted. Is this something to bring up with the shop guys?

The car has a new voltage regulator and a new generator.
 
Ed, 1100 RPM sounds a little high, both for idle RPM and for the ignition light to illuminate.

The reverse current cut-out lives in the voltage regulator housing, and I would think that a new one might need adjusting.
 
Ed,
I agree with twosheds, you should not get reverse current (light) even at idle. I don't know how much of this you want to do yourself, but there are a few checks that you can make with a voltmeter.
First, determine that everything is working ok at speed. Simply put the meter across the battery terminals with the engine at speed. You should show 14 volts. My guess is that you will show less than that at speed too.
Then you can ground the field on the generator (a bit more complicated) to see if it is weak. Here’s how (and regulator adjustment too): mechanical regulators
Tom
 
That description doesn't really sound like cutout adjustment to me. Pretty much regardless of adjustment, it shouldn't open until the generator is drawing current instead of producing it, and mine will put out a modest amount of current at 1100 rpm.

I'd start by checking the generator mounts (very common for the front lower mount to work loose) and belt tension. Also eyeball the wires to the generator for any cracks or kinks (an unexplained kink may indicate wires broken inside the insulation). Then I think I'd try to double-check the tach with a modern digital tach. If it does read high, try loosening the cable on the back of the tach head and see if it drops a bit. If so, the inner cable is too long (and should be shortened immediately as the pressure will eventually damage the tach).

Does the generator work OK otherwise? How many rpm does it take to keep up with the headlights? Some of them just need a bit more rpm, so there may be nothing wrong at all.
 
TomMull said:
Then you can ground the field on the generator (a bit more complicated) to see if it is weak.
Click to expand...

<span style="font-size: 14pt">You'll be sorry !</span>

Not all regulators work the same; on the TR the field is internally grounded and the contacts in the regulator connect the other side of the field to the output terminal. Trying to "ground" the field will at least cause it to stop working entirely, and at worst damage the regulator.
 
I see that I definitely may have to leave this to the experts at the shop, but at least I now have some ideas of what to ask and what to look for. Many thanks.

The generator keeps up very well (I think) with the headlights. When they are on, and I am running (about 2000 rpm), the ammeter registers about zero.

The belt is tight, and the generator mounting bolt is firm. The small wire going into the generator is bent at an extreme angle, but doesn't appear to be broken.

The tachometer has just been rebuilt and recalibrated.

It's possible that the guys who installed the regulator did not adjust it properly. There have been problems with it from the start. I'm thinking that I might just replace it with a new Moss pre-adjusted and cleaned regulator (I have a back-up) and hope that takes care of any regulator problem. I am assuming that it is possible just to "plug in" the new pre-adjusted regulator and drive off without any other adjustments, but I'm not sure about this.
 
Randall. I checked the points gaps in the voltage Regulator and they are right on the mark. I checked the continuity from the field connection on the voltage regulator and the generator, and got a clear signal that there are no breaks.

Battery is new, generator is new, battery cables are new, all cables and grounds have been checked and cleaned, generator mounting bolt is tight,belt is tight, tachometer is rebuilt and recalibrated.

If I can't discover why the ignition light comes on at 1100 revs and below then I'll probably install the new, factory adjusted and cleaned voltage regulator. My only question: do I need to adjust anything more on the regulator once the factory adjustment has been made? I know that I don't have to set the polarity on the regulator, so I should just be able to "plug and go." (ha, ha, ... that'll be the day).

I am also tempted to install one of those electronic regulators, but everyone I talk to hereabouts advise against it because they say they are no more reliable than the older ones.
 
John,

Thank you very much for the lead. The article looks very informative, and I will read it with care.

The ignition light does go on (at about 1100 rps and below) and off (above 1100 rpm, so it seems to be ok, except that I think going on at 1100 rps is a little high.

The generator is new (about 9 months old), so unless there is a defect, I think the problem isn't the generator. I'll try to get someone to adjust the regulator (it's still a bit beyond my skill level) or I'll install my back-up Moss adjusted regulator. The regulator on the car now is new (installed when the new generator was installed), but may be out of adjustment, as you suggest.
 
TR3driver said:
TomMull said:
Then you can ground the field on the generator (a bit more complicated) to see if it is weak.
Click to expand...

<span style="font-size: 14pt">You'll be sorry !</span>

Not all regulators work the same; on the TR the field is internally grounded and the contacts in the regulator connect the other side of the field to the output terminal. Trying to "ground" the field will at least cause it to stop working entirely, and at worst damage the regulator.
Click to expand...

As the link points out, you ground the field on the generator by replacing the field wire to the regulator with a jumper wire to ground. I've done it. No Ill effects. Tom
 
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