Fiesta not charging problem, puzzling problem

I'm getting a bit desperate now, I hope someone can help me...

I've got a Fiesta 1.8D, 1996. Earlier this week, the charge warning light came on (well, half on) whilst driving home. It was also obvious the thing wasn't charging, as my lights had faded by the time I got home.

I started looking at it his morning. I disconnected the alternator completely, and (perhaps fortunately) noticed that the charge warning light was still glowing, partly. My understanding is that it shouldn't do this, as the current that goes through the warning light goes through the alernator field coils to energise it.

The voltage at the alternator end of the field wire is only about 6, and this never seems to vary, whether the engine is running or the engine is stopped. Again, my understanding is that this is wrong, and while the field voltage may be about 6 when the alternator is stopped, it should go up to about 12 when the alternator is running.

I've tried to check the wire from the warning light to the alternator but the wiring diagram shoes a diode in it, and my meter won't read the resistance properly. It does show continuity as OK. (And another problem I've spent hours trying to solve: where the hell is this diode? I can't find it to check it.)

Finally, I briefly tried a wire straight from the battery live to the alternator field connection and this started the alternator charging. This tends to make me think the alternator ISN'T faulty, so I'm loathe to shell out for a new one just yet.

Can anyone assist with a diagnosis, and save me some £s, I hope.

Regards Chris

BTW, if my email address needs correcting if you want to use it.

Reply to
Chris
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Lots of vehicles work this way, but it depends on whether there was an engine run relay fitted. Ford certainly controlled the warning light, and any heavy loads that had to have the alternator charging (heated windows etc), by fitting a relay into what would of been the warning lamp circuit. I'm sure ford only started doing this on later vehicles, but it is something worth checking on a wiring diagram.

The easiest way to check this, is by disconnecting the lead off the alternator (you are disconnecting the wanring lamp wire, and not the field/rpm sensing wire?), and touching it to earth. Connected to earth, the light should be lit up fully, and connected to battery positive, the light should go out. If this test works, then the warning lamp circuit is fine, and it's a fault with the alternator.

The extra surge of power by doing this, may be enough to kick a dying alternator into life. The ideal way to test this, is to connect up to this terminal using a bulb (ideally 2.2W, but 5W is just as effective) from the battery positive. If everything works, then alternator is fine, but if not, it's time for a new alternator.

Reply to
Moray Cuthill

As Moray says there may or may not be a Run relay fitted to the charge warning lamp circuit, but whichever, your symptoms point to a partial short to earth (probably through something else as you have a dimly lit bulb) after the bulb,

The circuit is +12v ->ignition main relay -> bulb -> alternator -> earth.

When the alternator starts charging that end of the circuit goes from 0v up to +12v, so no current flows and the bulb goes out.

This will be something fairly simple like a chaffed wire, but will be a complete bitch to find!

It may be easiest to run a new wire from the instrument panel bulb direct to alternator, if only for testing purposes.

Tim..

Reply to
Tim (remove obvious)

"Tim (remove obvious)" wrote in message news:dmtmd2$7o5$ snipped-for-privacy@nwrdmz02.dmz.ncs.ea.ibs-infra.bt.com...

I can't remember if the fiestas used a similar wiring layout, but on escorts, the warning light wiring (ran in a seperate lomm to the main output) used to break where it went along and up the radiator support frame.

Reply to
Moray Cuthill

Of, course, a separate lead!! Why didn't I think of that - could have saved hours of faffing. Anyway, I tried that, and the bulb didn't go out, so I guess the alt. is the problem.

By the by, I did try tracing the wire from the warning bulb and (if I traced it right) the wire doesn't go to the alternator, but to a relay, so it's likely Moray is right, and there are other bits hanging off that circuit. The diagrams I have are supposedly for this model, but they are only Haynes, and I have found them to be wrong on other occasions. I looked at some other Fiesta models, and did find a relay for controlling the rear windscreen heater, so I guess mine has that relay as well.

Thank you for your help, gentlemen,

Chris

Reply to
Chris

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