Ignition light Issue

[DazbodS2]

Hi All,

Looking for some help again. My red ignition light has suddenly started to flash, albeit faintly and intermittently when the engine is running. The voltage gauge seems to indicate all is ok with the battery charging which to me suggests the alternator is working. All other electrics seem to be working ok. Any thoughts please?

In addition, I note in the circuit diagram there is a “3AW ignition warning light” unit forming part of the associated circuitry. What is it and where is it located?

Thanks

Darren

[david muir]

Had this! Put new brushes in alternator, easy and cheap!

[AshM]

Hi Darren

My similar car to yours developed the same fault.

Replaces the 3AW module with an updated one from SNGB and it resolved the flicker.

Sits above the voltage regulator where the main loom exits into the engine compartment.

Bolted to the frame/bulkhead in this picture (brown circle towards you).

Hope it helps.

Cheers
Ash

[malcolm]

Mine's been flashing from the day I bought it - about 7 years ago? Alternator charging well though, battery fine, so ignore it. If it came on permanently I'd do something about it. Think lots of people have experienced this

[DazbodS2]

Hi Dave, Ash and Malcom,

Many thanks for taking the time to reply. This is a new fault and has just started this week. The 3aw unit is I suspect not original. It’s a small 1” or so cubic plastic unit with a potted base and three flying leads exiting it located as Ash stated. I understand it is effectively a bimetallic strip that switches the light on when no charge from the alternator is present by grounding one side of the ignition bulb. Will investigate its replacement and the bushes as suggested. Is it fair to say I can rule out the voltage regulator?

Thanks all again.

Darren

[Gfhug]

Darren, you might like to read this topic of changing the alternator to a self-regulating one:
viewtopic.php?f=5&t=18033

Geoff

[angelw]

Darren Wrote:

The 3aw unit is I suspect not original. It’s a small 1” or so cubic plastic unit with a potted base and three flying leads exiting it located as Ash stated. I understand it is effectively a bimetallic strip that switches the light on when no charge from the alternator is present by grounding one side of the ignition bulb. Will investigate its replacement and the bushes as suggested. Is it fair to say I can rule out the voltage regulator?

Hello Darren,
Yes, you can rule out the voltage regulator as far as the ignition light is concerned, as this is controlled by the 3AW. The 3AW you described is an After Market device and its a fair chance that it's not of the same construction as the original device and is highly likely to be a solid state unit. When a solid state unit fails, its more like turning off a light switch than a gradual failure.

I would be testing the voltage on the Alternator wire that connects to the "AL" terminal of the 3AW unit, before swapping out the 3AW. The voltage should be circa 7VAC.

Regards,

Bill

[DazbodS2]

Thanks Geoff and Bill for your further comments and information. The 3AW unit I have fitted is indeed an aftermarket unit and looks to be one of the two options supplied by SNG. I thought it would be a simple and cheap first step to replace the bushes as suggested. Unfortunately, SNG and Martin Robbey both state the bush unit is no longer available - any ideas as to whether the unit can be obtained? Also can you still obtain period wiring looming tape (if that’s what it’s called) as all the wiring has been rebound in the stuff and will need to be unwrapped and rewrapped as part of this excercise?

[malcolm]

I'm no expert, so check this out first, but I believe you can turn the bushes round and get loads more life from them.

[Allrand]

David said new brushes, not bushes.

[malcolm]

David said new brushes, not bushes.

I meant brushes!

[Allrand]

[MCY44H]

I have also had this issue with my S2 since I bought it nearly five years ago. I have similarly replaced various components, including the 3AW, all without success. However, someone on another Jaguar forum has suggested that while the generator light comes on if the voltage drops below a certain value (8v?), it also flickers if there is too much voltage being applied by the alternator. One of the respondents suggested turning on the headlights lights to add load, which will reduce the voltage. I think this has already been mentioned above. When I do that, the problem goes away. Since I live in the country and my Roadster is delightfully camouflaged in BRG, I drive around with the lights on all the time and my flickering genny light is no more.

All this is hearsay, but I tried a couple of tests today in the garage when doing my fortnightly start and run up. On my car, the number of cranks to start it is equal to the number of days it goes without starting, so fortnightly seems like a kind interval from a battery perspective. I decided to investigate, because I have recently purchased a cigar lighter USB charger which also conveniently records voltage and (less helpfully) the temperature. I have an Odyssey PC1200 battery fitted (which I strongly recommend).

So, with my CTEK charger still connected (not sure that was great idea to be honest), I start the car. The voltage hits 14.4V on my cigar charger and the genny light slowly starts to flicker. Switching on the main headlights makes the flickering go away, as usual. Turn them off and the flickering restarts. Revving up the car to 2000RPM, the voltage increases to 14.9V and now the generator light is burning continually.

I disconnect the CTEK, and the voltage falls back to 14.2V and the ignition light goes out. I try various combinations with headlights on and off, but no ignition lights come on. It looks like the flickering may start at about 14.4V.

While this is not conclusive, it seems to add credence to the notion that overcharging, or at least high levels of charging can set off a flickering ignition light on an S2. I shall continue to drive around with my headlights on, which seems to be the cheapest way of fixing the problem. My battery is four years old and remains in fine health, so I’m fairly comfortable that this is not a big deal (famous last words!).

[johnetype]

The original 3AW was an electro-mechanical device which by its design couldn't cause flickering of the ignition warning light if the alternator exceeded a certain voltage. It also wasn't a very reliable device and has been unavailable in its original form for many years during which time several substitutes relying on electronic components inside to do the same job have appeared on the marketplace. It would appear that some electronic 3AW replacements weren't that well designed leading to reports of flickering and other maladies.

Clearly your alternator is working from your voltage readings so the issue is simply your particular 3AW.

Ash made a recommendation above saying that his 3AW doesn't flicker so I'd suggest trying one from the same source if the flicker bothers you.

[MCY44H]

If it is the 3AW, then I have three flickering miscreant devices, one of which the previous owner put on in 2002 and two I bought recently trying to get to the bottom of the problem. I don’t feel motivated to have another go at the lucky dip.

Still, its been better for me than oil pressure senders. I have four of them and one nearly works! I have to persist with them because the wet gauge (that worked beautifully) sprung a leak and sprayed hot oil around behind the dashboard. My wife refused to get in the car until it was changed.

All good fun!

[johnetype]

It is ironic that you've encountered the two most unreliable sensors on a Series 2, the oil pressure and 3AW although the 4TR isn't that far behind

The good news is that you can unplug the 3AW all together and live without it. Your alternator will continue to work fine. You already know how to measure the output voltage or use the voltmeter in the dashboard to tell you if the alternator is still working and you'll get no more flickering ignition warning light.

[MarekH]

Everything you need to know about this topic is on the coolcatcorp.com website. The conclusion you will reach is that the 3AW is pretty useless as a diagnostic, even when working as it is meant to.

kind regards
Marek

[Mickey]

Darren,
The ignition light on my '69 FHC has glimmered from time to time. But recently it began glowing steadily. Can you provide the part number for the 3AW from SNG? And did that solve your problem? Thanks!

Mickey

[Gfhug]

Searching their website for 3AW gives: BMK1092J

Geoff

[Stevedavies]

The 3AW unit was a fragile component. I replaced the ignition light with an electronic version. This is used on motorbikes and is a led which has a built in voltage ripple detector ie it detects the ac to dc conversion performed by the alternator. Normally the light is powered on. When the car starts then the voltage ripple is present and the light turns off. Led fits in the speedo housing. Great low power, reliable replacement for the ignition warning light