3AW relay

[Heronscourt]

The ignition light on my series 1.5 stays on when the engine is running, even when at 4500 rpm.
With the engine off the voltmeter shows 12.4 v, engine running shows around 13.6 v, so I deduce that the alternator, 4tr unit and alternator relay are all functioning correctly.
Reading coolcats.com article on the alternator and its associated relays it says that on the 3AW ignition light relay testing across the AL and E terminals should show resistance of between 16 and 20 ohms, outside this value the relay is faulty. Testing across the WL and E terminals should show close to zero ohms.
My brand new 3AW shows 14 ohms and zero ohms respectively for the two tests.
Is this sufficiently out of spec to prevent the ignition light going off when the engine is running?

[MarekH]

Put a 16-20 ohm resistor in line with the suspected faulty unit and you'll have your answer.
kind regards
Marek

[Heronscourt]

Thanks Marek, I tried that and it seemed to show the 3AW was ok but I borrowed a good 3AW and also tried a solid state 3AW but I still have ignition light on with engine running. The voltmeter shows just over 12volt without the engine not running and nearly 15 volts with the engine running
I’ve checked wiring to the alternator relay and 3AW relay. Am I correct in assuming that as the light remains with the engine running the problem is likely to be earth related



.

[MarekH]

The 3aw is a relay which expects 7.5v ac on its AL terminal to flow through to the chassis via its E terminal. When that happens it disconnects WL from E. That means a circuit is broken, so the 12v ignition light bulb loses its path to earth and extinguishes.


If the 3aw resistances check out, then the bulb not going out is because

1/ the AL terminal of the alternator doesn't deliver 7.5v ac to the 3aw AL spade.
That suggests 1a/ a poor connection between alternator and 3aw or 1b/ a bad diode so you don't have the right input into the 3aw.

or

2/ the 3aw is incapable of dropping the WL to E connection because those terminals remain shorted internally inside the 3aw for some reason.

or

3/ you have accidentally shorted the 3aw side of the warning bulb to the chassis anyway.

kind regards
Marek

[Heronscourt]

Thanks Marek, I’ll check those points out starting with the 7.5V ac output. At present that’s the main suspect

Alan

[Heronscourt]

I’ve checked the AL pole output and have zero volts ac but the battery is charging at 14.2 volts dc. There is no grounding at the ign warning light bulb so am I correct in assuming that all the diodes are ok as rectification is taking place and that the problem is probably an internal connection to the AL pole inside the alternator. The insulator to the pole is correctly in place..