Ignition light flickering - CURED

[JerryL770]

My ignition light flickers all the time so I decided to investigate. It's on solid with no engine running, then flickers even up to 2,000rpm.

My car was restored in 2017 with new wiring and an uprated alternator. This alternator has only 3 electrical connections, a heavy brown, a lightweight brown and a brown/yellow.

I think the lightweight brown goes to the 4TR and, having checked, the brown yellow does go to the 3AW unit. What then perplexed me is that, the brown/black wire on the 3AW (which seems to go to the ignition warning light) is piggybacked onto the brown/yellow connection on the AL terminal of the 3AW unit. There is no wire on the WL terminal.

So, should I move that brown/black onto the WL terminal on my 3AW?

[politeperson]

Is the light shared with your oil pressure sender?

[JerryL770]

Is the light shared with your oil pressure sender?

No, it's a 1970 S2 car. They are completely separate.

[malcolm]

I don’t know the answer, but my ignition light has flickered ever since I’ve owned the car (11 years) and I know the alternator is fine so I ignore it. The relay was changed recently and the flickering stopped for a few months, now it’s back!

[angelw]

Hello Jerome,
Your car should be equipped with a 3AW device that the Ignition Light sources ground through when the Alternator is not charging. The ignition light is extinguished by the source to ground for the light being interrupted, which is brought about by 7VAC being supplied by the Alternate. via the AL terminal on the 3AW device. Accordingly, your issue will either be a faulty 3AW unit, or the required feed is not being supplied by the Alternator.

Is your Alternator actually charging the battery?

Regards,

Bill

[mgcjag]

Jerrey....you said above that you have a replacement alternator(3 wire). Typically it dosnt use the 3Aw unit....a wire goes direct to the ignition warning lamp....current drawn through the lamp exited the alternator to allow it to charge....either you have a faulty alternator or ignition lamp(What wattage bulb does your alternator need) .....if an led is used as the warning lamp not enough current is drawn by the led so the alternator dosnt charge...Steve ps have a read here viewtopic.php?f=5&t=18033&p=146696&hili ... de#p146696

[JerryL770]

Thank you Bill and Steve for helpful advice and link which has likely answered my question though I am also just now still slightly perpelexed.

Like Andy, I don't like having to grope around back of the dash but I have just had to do so to replace my tacho which I sent to Speedograph Richfield for conversion - subject of another thanks post to come

My alternator, pictured here

20250226_093605s.jpg (133.3 KiB) Viewed 56719 times

charges my battery OK, voltage on my gauge is OK. The wiring harness is clearly built for a 3 connection alternator.

This is my 3AW which it seems I don't need and is only there to be "original" and hold the wires safely

20250226_093553s.jpg (127.36 KiB) Viewed 56719 times

So I need now to see what bulb I have in the ignition warning light and this I was reluctant to pull out - just now.

20250226_093726s.jpg (96.72 KiB) Viewed 56719 times

Why? Because as you can see, there is nothing to hold in the bulb for the low fuel light, except pressure from the wiring. However, bite the bullet and pull the ignition bulb and the holder has the proper retainers and the bulb is indeed a filament bulb of 2.2W.

Is that enough? Can I get a higher wattage bulb? Should I ??

[mgcjag]

The bulb I can see looks very much like an led....I can i see yellow led,s?...or am I mis seeing it....try a 5w bulb or look up the alternator spec..typically you need about 1/3 amp...your 2.2wat bulb is I think a bit low
Steve

[JerryL770]

Thanks Steve.

Yes indeed, the bulb you can see in my picture is an LED but that is for the low fuel level warning.

My alternator is charging OK so why would a larger wattage bulb no longer be lit up when the engine is running. Is this then an alternator problem?

I cannot see any makers marks on the alternator so difficult to get a spec for it. I'm assuming the 4TR is still functioning. It is certainly connected. Maybe the alternator is not self regulating and the 3AW should have the brown/black on the WL terminal ??

[mgcjag]

I think you need to work out exactly what you have and a drawing of how its wired....with a 3 wire alternator typically a 4tr and 3AW in not needed....Steve ps a flickering bulb could be the alternator, bulb or wireing/eth ect

[david.coan]

FYI- My 3aW relay is an electronic version, i fitted it about 6 years ago, along with an uprated alternator, the relay i bought has a feature that if it detects the voltage is near 14v it flashes (flickers) the ignition lamp to warn you of potentially high volts, if the fans start up or i turn on say the heater fan or any lights etc it drops the voltage enough and the flickering stops. So my flickering is not something i am concerned about.

[JerryL770]

Yes, we have cured my flickering ignition warning light. It now comes on clear with the ignition on and goes out fully as soon as the engine is running.

The cure? With a self regulating alternator the Ignition light connection on the alternator is to be connected directly to the ignition warning light. The 3AW relay is no longer needed. This was accomplished by a piggy back connection of the wire from the alternator to the warning light wire terminal at the 3AW relay. This piggyback junction was fitted to the terminal on the 3AW, just to keep it safe, I guess. The cure is to remove it, cover with shrink tube and secure out of the way.

Because the earth lead was still connected to the 3AW this was allowing some current to flow through the 3AW from the warning light side allowing the flicker.

[Dr.No007]

Good morning, very interesting thread I came across while searching for solutions to my flickering ignition control light. I still have the original alternator and the 3AW. My ignition control light flickers almost constantly, but goes out as soon as I turn on a consumer, such as the fan or the lights. By the way, there's a black (useless?) cable hanging around the 3AW/4TR area that's not connected. I've attached a few pictures. Could the 3AW be the cause of the flickering? What does the brown cable mean? Does anyone have any ideas?

Best regards, Klaus