Ignition warning light stays on

On my early 69 S2 the ignition warning light stays on all the time. I have read much information in the archives and the wonderful articles by Mike Frank that explains how the 11AC alternator works, and the function of the AL signal:

I have 14.5 volts at the battery with the engine running. I removed the 3AW relay and tested it according to Mike Frank that is within spec. I disconnected the wire from the AL terminal on the 3AW relay and with the engine running it is reading over 14 volts AC. I understand the the voltage at the AL terminal should be between 7-7.5 volts AC.
The alternator is only 11 months old and still under warranty. Before I return it to the vendor I just wanted to verify that it is out of spec and probably causing the problem. To confirm my readings I had it tested by a local electrical house and they verified that the AL terminal on the alternator was producing 14.8 volts AC.

Thanks for your help,


The light on my series II also stayed on after replacing the alternator and 3AW. I am sure I wired up this thing wrong somewhere. Like you have 14+ volts and no charging problems resolved the glowing bulb by just removing it.

Andy, I do not know this first hand, but somewhere I read there are several different stators available for this alternator, and the wrong stator may cause high AL post output, possibly causing your issue.

Are you sure your meter is on the AC setting?

Frank, just to make sure that I my meter was reading correctly, I drove the car to my local electrical repair shop that specializes in repairing motors and generators and I had him test it for me. He removed the lucar connector from the AL terminal on the 3AW and tested it at the lucar connector to ground and then tested the AL terminal on the alternator to ground and got 14.8 volts on the AC setting on his multimeter which is way more expensive than mine. He verified that it was set to AC, thanks for asking. He thought that one of the stators could be malfunctioning.

Very strange. What are you seeing on DC?

I have resolved the issue and thanks to everyone for your input. It was not the alternator or the 3AW relay both of those parts are OK and working correctly.

The problem was with the ignition light bulb holder that snaps into the back of the speedo. I recently had my speedo recalibrated and when I put the ignition light holder back into the speedo I bent one of the prongs so it was touching the inner part of the bulb socket causing a short to ground all the time. So the ignition light never went out.

The batteries in my multi-meter were low so it was reading incorrectly. I don’t know what happened with the electrical repair guy’s meter.

Thanks again for your help and I wonder if Glenn (melloyello) has the same problem.


Just checked the socket for a short, no luck.

I recently fitted a Solid State replacement for a 3AW to an S1 2+2 nearing completion at my works. This car originally used an oil pressure switch to extinguish the ignition light, which is no indication whatsoever as to whether the Alternator is charging or not. The logic used with this system is that:

  1. If there is oil pressure and therefore, the ignition light is extinguish, then the engine must be running.

  2. If the engine is running, then the Alternator must be charging the battery, irrespective of whether an Alternator or other battery charging device is actually attached to the engine. It could, for example, be stored safely in the boot area of the car, in its original packing case. However, I digress; back to the 3AW.

The car has been fitted with a complete, new wiring loom and as the wiring infrastructure is there to accommodate a 3AW, the client sourced a Solid State unit by Retro Classic Car Parts. So cutting to the chase, after correct fitting, the ignition light stays on.

The alternator is working correctly, with measured 14.6VDC at the battery and 8VAC from the lead that connects to the AL terminal of the 3AW. The following was tried:

  1. A known working, conventional 3AW was installed; it and the ignition light behaved as they should.

  2. The Retro Classic unit was reconnected and 12VDC supplied to the AL terminal; the ignition light immediately went out.

  3. Alternating between connecting and not of the 12VDC supply to the AL terminal had the Retro Classic unit behaving as it should and the ignition light also functioning as it should.

  4. Connect the lead from the Alternator, emitting within close tolerance of the specified 7.5VAC and the ignition light stays on.

If you launch https://www.retroclassiccarparts.com/ it diverts to https://www.holden.co.uk/

As this is a new unit, I contacted the supplier on behalf of the client, explaining the situation and requesting advice; following is what I’ve heard thus far from the four messages and emails sent over four weeks:

Clearly they’re more focused on selling than service.

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Bill, I am not sure that number 2 is the logic behind the “ignition” light.

  1. Agreed, when connected to the oil pressure switch, the light goes out when the engine is running. Note, it is called an ignition light to warn the ignition is on when the engine is not running. It is not called an oil pressure light, as it is not there to indicate if the engine has oil pressure. There is an oil pressure gauge for that.
  2. When connected to the alternator, its purpose again is to let one know the ignition is on when the engine is not running. It is not there to let one know the charging system is operating properly. If it was to indicate charging, it would be labeled charge, alt, gen, bat or something. There is an ammeter or voltmeter gauge to indicate whether the charging system is operating properly.

It is unfortunate and frustrating when contacting a vendor is difficult. Hope you get some results soon.

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Bill, you can buy a Jaguar 3AW from Welsh Enterprises for $53 part # C24169. Probably better than the frustration you’re having with retroclassicparts.

Andy 69 FHC

Thanks Andy. I have alternatives and the manufacturer of the retroclassicparts 3AW, who saw my Post, has been in touch; kudos to them, but not the supplier.

What pisses me off is when its clearly obvious that the supplier is far more focused on sales than service and the product. One organization that sent me a part to evaluate and critique, are selling the part after I advised them that the part will not assemble and is not fit for purpose. Its one thing to be selling an item when you’re ignorant of its fault, but entirely another when you market the item knowing that its not fit for purpose.



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The ignition light on a 3AW equipped E-type does have value diagnosing the charging system. If the alternator stops charging, the voltage on the Lucas 11AC alternator AL terminal will probably drop below ~7.5 volts, and this will trigger the light. The 3AW extinguishes the light when the voltage reaches that approximate voltage range.

It personally did alert me to a charging failure. In another thread, I asked about why my ignition light was always on despite the installation of a Coolcat solid state 3AW replacement (which I highly recommend.) I had the alternator checked out, did a variety of charging tests, etc. and all seemed fine.

As it turned out, somehow I had ordered a positive ground 3AW replacement instead of a negative ground, and this meant my ignition light was always on despite proper operation. This was easily addressed and it worked perfectly.

A few days after taking my first long (450+) mile drive, the ignition light came on and stayed on while running, at all RPMs. All checks (including voltage regulator bypass) showed low charging voltage (~12 volts) everywhere, and an external ammeter showed little output. I dropped off the alternator at the same shop that cleared it a few months before and they confirmed it had gone bad and wasn’t putting out any juice.

The built-in ammeter didn’t swing sharply to the left or anything like that (perhaps it is unreliable or I don’t know how to read it correctly.) The only way I would have known there was a failure was seeing the ignition light illuminated when the engine was running. So I attest to its value as a warning device.