Ignition light on.
 

So the ignition light is constantly on but the alternator is charging the battery . Battery voltage engine off 12.6v engine running 14.8v. Ford 302 single wire alternator Proform 100. Voltage on red cable to lamp engine off 12.6v running 14.8v. Other cable to lamp (blue) goes to earth both with engine off and on. Explains why ignition light is constantly on. Question:is there anything else I can do or as I suspect take the alternator off to be tested for a low voltage return. Must admit I don't really understand how single cable alternators work. Any help appreciated. My local auto electrician says a single terminal alternator can’t support an ignition warning light and must be another warning light such as oil pressure but it hasn’t got an oil pressure light just a pressure gauge. Thing is it used to go out with the engine running then became intermittently on before being permanently on.
Dek

Your local auto electrician is correct. The circuitry for the ignition or electrical warning light is no longer present in the alternator if it is a one-wire configuration.

What I can’t understand is why I had an apparent ignition light which came on with the ignition and went off with the engine running.

Perhaps it is an oil low pressure warning light. Check for a T-fitting on the oil pressure port with one sender for the gauge and another for the light.

Yes I have Tommy. Just the oil pressure port with no electrical sender. The only sender I have is the water temp.

I see you are in the UK. Perhaps that light warns when one of the Lucas wires is low on smoke. ;-)

Do you have a remote oil filter or cooler that might have another oil pressure port?

One side of the Alternator light should go to the battery via ignition switch.....and 5he other side of the alternator light should go to the alternator.....

When key is turned on the light lights up because it has a potential of 12 volts on one side....when the alternator starts putting out 12 volts or more....then the light has 12 volts on both sides of the light and consequently zero potential & the light goes out.....

You have three alternator design choices. If we use connecting wires at the alternator to identify each type, the three alternator types can be described as 1-wire, 2-wire, and 3-wire alternators.

1-WIRE ALTERNATORS

The 1-wire alternators are what is termed self-exciting. A self-exiting alternator is an alternator that has a specially modified voltage regulator that doesn't need a 12V ignition wire to activate it. The voltage regulator that controls the alternator output contains circuitry that uses the residual magnetism in the alternator's rotor fields to determine when to turn the alternator on and off. The regulator does this by sensing the alternator RPM; when it reaches a threshold RPM, the voltage regulator "turns on." Using this type of alternator, you would start the vehicle, rev the motor slightly, and the alternator would begin charging. Some Delco-based alternators, with a self-exciting voltage regulator, do not need you to rev the engine.


2-WIRE ALTERNATORS

Most standard alternators will use a two-wire setup. Two-wire alternators use the primary battery wire to the back of the alternator and also the ignition wire to activate the alternator. This setup allows the alternator to start charging as soon as the engine is running.


3-WIRE ALTERNATORS

Three wire alternators use a battery wire, ignition/warning light wire, and voltage sensing wire. Three wires in all. This is the design you want to use if you intend to support an ignition/warning light.

Voltage sensing is used when you want the alternator to read voltage at some other point than the battery, for example, when an extended length of cable is required to reach the battery. An excellent example of this would be a trunk-mounted battery.

You can use a self-exciting alternator with a trunk-mounted battery, I do. If you choose to use the self-exciting style alternator and it is based on almost anything other than a Delco CS series design, you will need to blip the throttle to get the alternator charging right after starting.

I use Denso internals with square wire and a hairpin winding in the small Ford 6G “T” mount case configured as a six-phase device because of both space requirements and the power budget forced on me by choosing a supercharged Modmotor. I set the engine start-up in my ECU to momentarily rev the engine to about 1500 rpm at start-up and then quickly return to normal idle. That immediate jump-up in engine speed at start-up turns on my alternator, so I don’t need to remember to blip the throttle.

While I have not tried the approach Morris has suggested, it logically sounds like it should work. When I did my electrical system, I didn’t think deeply enough to noodle out Morris’ solution. I do like it, and intuitively it does sound like it would work.

Disclaimer, I am not an electrician, and I don’t play one on TV ...

Actually, the best and easiest way is to eliminate the light and just us a 12 VDC volt gauge and when the alternator starts charging the Volt meter will go up to 14.5 and at idle it would be 12.5 volts. Anything other then this is a issue.

It only cost $90 or $99 (can't remember which anymore) from Nisonger to do just that, Morris. An extra added attraction at no extra cost was the fire fear factor associated with the amp gauge that disappears when the volt gauge replaces it.

No none of those.

Thanks Morris. I did also look into this and found exactly what you described and understood it but then things got more complicated when I discovered I had a single terminal alternator.

Thanks Ed for that master class in alternators. Every day is a school day!

Actually Morris I have got a voltmeter fitted so it’s not a big deal. Unfortunately it’s situated on the passenger side in the Daytona and not immediately in front of me like the ignition light. There’s nothing like a warning light to grab your attention. Perhaps I should disconnect it in the interim and rewire it as an oil pressure warning light to give it some function?

Morris, meant to ask what’s with the green twine? Wind testing?

The reason I kept coming back to the possibility of your red light being for low oil pressure is that I've had a big red light directly in front of me for that reason in my last two cars. It started when I lost oil pressure during some hard turns at an autocross and sheared the distributor gear. Losing alternator power is not something that demands immediate attention, but losing oil pressure is.

Appreciate that Tommy but oil pressure showing ok on the gauge.

Aerodynamic testing.....