The 'E' Type Forum

I thought I'd do a little write up about something I've made work on my car, not because its particularly earth shattering but mostly because of the excellent customer service I received for an order of <?20 delivered.

Problem:
My ignition warning light didnt work, and the problem wasnt the lamp!

Diagnosis:
The warning light is controlled by a Lucas 3AW relay, a can shaped relay in my car LHD FHC positioned near the battery and looking not unlike a flasher relay.


I couldnt find a diagram of what the 3AW actually does, but I checked that it got its AC feed from the alterator, its DC feed from the fusebox and was adequately grounded - and so I concluded that it was failed. Quick google and I discovered that they were available either as like for like replacements or solid state aftermarket, and also that they were orginally fitted on Norton Commando motorcycles - this piqued my interest so I googled on, and found the website http://www.improvingclassicmotorcycles.com/products.htm and I watched their video:


I pinged them an email, we struck up a conversation and the chap, Graham, really went beyond the call to make sure I got the the right product. The lamp goes into a 16mm (approx) orifice, and so we hatched a plot to deal with that. (sorry, I am metric when it comes to measurements less than a mile)


I ordered, and a few days later the product arrived:


Graham had supplied a bit of PVC tubing, which I split and bound making 16mm:


One cable on to the ignition switch. ( I did tidy it up later) I can't I confess tell you which terminal thats on, but my understanding is that my ignition switch only has (effectively) 3 terminals "in", "run" and "start" so I just looked for "run" with my multimeter, and piggy backed off that, it was easier than removing the switch. (the bullet connector disconnected in this photo is the feed to the worlds most annoying key in alarm - I did restore it once finished but its a more peaceful day with it off)

and the other on to a ground.

Cable tied the rest of it away:


and job done.

I should add that the original wiring to the 3AW Relay remains on my car, I have simply isolated the ends, ditto I have retained but tied out of the way, the original lamp holder for the warning light so this is entirely reversible should a future custodian want to re-establish it. But, I think this unit actually gives me better data, so I'm happy.

So, OK, I havent done rocket science, or new art, but what impressed me, as I said above, was the care an attention Graham at http://www.improvingclassicmotorcycles.com/index.htm took in the process making sure I got the right product, and that I thought needed sharing.

Thanks.

Hi Matt...have i missed something....you connected one wire to the ignition switch and one to ground......you dont mention tbe one to tne alternator....how many wires do you have to connect

From what one can see of the instructions I get the impression that this is not in fact an alternator warning light at all, but is a battery low / high voltage light. Since the S2 has a voltmeter anyway, I cannot see that it adds anything to the knowledge already available from the instruments , and it certainly does not seem to fulfil the major function of the AW which is to alert one immediately to belt failure


Edit : I take it back - see the explanation below. Very ingenious

Thanks for your replies chaps. I pointed the manufacturer at them, and his reply via email to me was:

"the CWL doesn't need to connect to the alternator. It's a small computer constantly measuring and analysing system voltage and can figure out if the alternator is working from that analysis. The CWL only turns the light off when the battery voltage shows it's charging AND when the CWL detects alternator ripple. As soon as the alt belt fails, alternator ripple disappears and the light comes on, even if battery voltage is high from being freshly charged."

On a practical level, I'm not near my car today, but if you want to suggest a cable for me to (safely) pull off to simulate alternator failure I'm happy to give it a go and report.

jellypig wrote: On a practical level, I'm not near my car today, but if you want to suggest a cable for me to (safely) pull off to simulate alternator failure I'm happy to give it a go and report.

Nice find and write up. Do not disconnect your alternator as it will fry the diodes, besides the explanation is good enough for me.

Thanks for the reply Matt.....sounds like a good little device

Moved here as it is a very nice upgrade. Ideal if you don't want to fit a voltmeter on your alternator equipped car.

jellypig wrote: ↑

Sun May 22, 2016 6:11 am

I thought I'd do a little write up about something I've made work on my car, not because its particularly earth shattering but mostly because of the excellent customer service I received for an order of <?20 delivered.

Problem:
My ignition warning light didnt work, and the problem wasnt the lamp!

Diagnosis:
The warning light is controlled by a Lucas 3AW relay, a can shaped relay in my car LHD FHC positioned near the battery and looking not unlike a flasher relay.


I couldnt find a diagram of what the 3AW actually does, but I checked that it got its AC feed from the alterator, its DC feed from the fusebox and was adequately grounded - and so I concluded that it was failed.

Hi - reviving an old thread. I am putting in a 3aw unit (not going into a Jag though) that I just purchased from SNG but am not sure of the wiring. It has three contacts 'AL', 'E' and 'WL' - I am happy the E is earth and AL goes to the alternator. It is the WL that I am not sure of.

In most modern alternators a 3aw unit is not needed and switched 12v (ignition) goes to the indicator light then direct to the alternator. In the earlier systems that use the 3aw is WL still the same, that is, switched 12v (ignition) goes to the ignition light and then to the WL contact on the 3aw unit. In the wiring diagram above the right hand side is missing and I cannot see if it is to switched power or straight to earth.

I assume that with the engine off and ignition on power runs from the ignition switch through the ignition light to the WL contact on the 3AW and and then to earth which lights up the ignition light. When you then fire the engine up and the alternator is generating power the 3aw unit picks up the 12v from the alternator via the AL contact on the 3aw and switches off the power coming from the WL contact so the ignition light then goes out.

I have I understood how this works correctly??

Thanks

Garry

With nothing connected to the Al terminal, the Wl terminal is connected to E the earth on the 3AW. So, if you have a ignition warning light with one side connected to 12 volts and the other side connected to the Wl terminal the ignition warning light will illuminate as it is being grounded by the 3AW unit.

The Al terminal on the alternator generates around 7.5 volts AC when the alternator is running. If this is connected to the Al terminal on the 3AW unit, it heats up a bi-metallic strip inside the 3AW and opens the connection between the Wl and E terminals which means if you have an ignition warning light connected, it will now go out. Remove the voltage from the Al terminal (alternator fails, fan belt breaks or engine stops) and the strip cools and remakes the circuit between the Wl and E earth terminals bringing the light back on.

If instead of 7.5 volts AC you apply 12 volts DC (or up to 14 volts if you're using a regular car supply) and connect it to the Al terminal on the 3AW unit it will heat up the strip and open it in just the same way, however I'd be concerned that now the thermal strip has 4 times the power being dissipated in it which means it will heat up a lot more and may well burn out or have a shortened life.

This is how the original 3AW unit worked. These days it's possible to replicate the 3AW functionality with a few electronic components rather than a thermal strip inside the can and be non the wiser from the outside. I do not know if modern 3AW units are the same inside as the originals so if the unit you've just got from SNG has electronic components inside it may be able to cope with 14 volts DC being applied to its Al terminal without damage. On the other hand it may not work at all if you don't supply an AC voltage.

Hi John - and thanks for that information - very informative.

I have tested the circuit you described and it works great.

Thanks

Garry