Alternator charge light peculiarity/problem.

[oldcorollas]

either find the Mitsu information, or go by the Bosch compact specs (as opposed to the old style specs..)
info available from bosch sites.

[Sam_Q]

Well, you sold me one without that information.

I tell you what, once you rev your mini engine to 8000rpm I shall give you a formal written appology!

oldcorollas: thanks I will do just that

[Slim]

It revs to 7000 happily. But yeah, i don't think it'd make it to 8k without a bang.

[DX20VT]

As I said before it will be a power supply to the bulb issue.

When the key is on and engine not runing, the alternator earths the wire.
Not a direct earth as it is through the rotor winding on one of those, but close enought to call it earth.
As you have no power to the bulb it does not come on,
Check.

When you start the engine the alternator will start to charge and put power out the warning light wire.
Normally this means that you now have 12V ign power on one side of the bulb
and 12V from the alternator on the other side
and the buld does not glow as there is no current flow through it.
Because you are missing a power feed to the IGN side of the bulb the bulb glows when the engine is running,
as there is power flowing through it backwards.
the fact the the bulb glows tell you 2 things,
1. The bulb is not blown.
2. It is connected to the correct wire on the alternator and the alternator is working.

To test this is really easy.
Turn on the ign but do not start the car.
Take the wire that goes to the warning light terminal of the alternator and touch it onto an earth, the alt body, alt mount, engine block etc.

If the light does not come on then ther is a fault in the car..

I am an Auto Elec and would almost 100% guarantee it is a fault in the car,
not the alt, and not the way the alt is connected.

[Slim]

Is it at all possible that the alternator can be damaged by connecting the L and R the wrong way round, or grounding something that shouldn't have, etc. ?

I have to wait until the weekend to have a proper look at things. I will have a look then with timbo and report back what we find out.

In the meantime, thanks to all for their input and info provided.