Technical How does the alternator warning light work?

[Jodiwe]

Hi guys,

Summary: Does the alternator kick in the usual old-style way using the alternator warning light to provide the initial rotor current? If not, how does it work with 2 terminals?

I've got a 1999 Uno 1108cc which I needed to replace the alternator on because it would not charge even when connecting the warning light connection (D+) to 12V. I couldn't find stock of Uno alternators, but I knew the Palio 1.2 has the same engine block, and I compared the two alternators at the spares shop and they seemed close enough (terminal sizing differences). After installing, the battery charging indicator light doesn't go out once the engine is running, but the battery is reading at over 14V, so it is charging. Is this alternator designed to be driven by the ECU and has a different way of determining a charging fault?

The new alternator is not an original Fiat part, so it's possible it's faulty somehow.

 

[bugsymike]

Hi guys,

Summary: Does the alternator kick in the usual old-style way using the alternator warning light to provide the initial rotor current? If not, how does it work with 2 terminals?

I've got a 1999 Uno 1108cc which I needed to replace the alternator on because it would not charge even when connecting the warning light connection (D+) to 12V. I couldn't find stock of Uno alternators, but I knew the Palio 1.2 has the same engine block, and I compared the two alternators at the spares shop and they seemed close enough (terminal sizing differences). After installing, the battery charging indicator light doesn't go out once the engine is running, but the battery is reading at over 14V, so it is charging. Is this alternator designed to be driven by the ECU and has a different way of determining a charging fault?

The new alternator is not an original Fiat part, so it's possible it's faulty somehow.

View attachment 417603

I can't comment about the Palio, but the way I understand it and was taught was that the warning light system was an important part of the charging circuit and that whilst an alternator may work for a while without it connected , eventually it will fail for some reason. I also knew that if you wanted a alterantor to start charging at a slower speed it was possible to put a slightly higher wattage bulb in the circuit, for instances if you wanted to retro fit an alterantor to an old diesel engine that previously had a dynamo fitted.
Not sure if any of this helps your problem, sorry.

 

[Jodiwe]

Thanks for that. It turns out I had bought a manual for the Siena / Palio a while ago, so I have some schematics to look at. Unfortunately it doesn't have the 1242cc engine, but this is the 1372 one:

It seems like there's a resistor in parallel with the instrument panel (55) battery indicator light. I can't see that resistor when I look at pictures of these instrument panels online. Are there other Fiats that have the same setup?

 

[bugsymike]

Thanks for that. It turns out I had bought a manual for the Siena / Palio a while ago, so I have some schematics to look at. Unfortunately it doesn't have the 1242cc engine, but this is the 1372 one:
View attachment 417617

It seems like there's a resistor in parallel with the instrument panel (55) battery indicator light. I can't see that resistor when I look at pictures of these instrument panels online. Are there other Fiats that have the same setup?

So not as simple as the earlier systems. See if anything in the down loads section.