Alternator wierdness

[julians]

I've just changed the alternator (because the bearings were starting to get very noisy), and now the red light on the dash wont go out, even though a multimeter shows the battery voltage around 14V with the engine running and around 12v with the engine switched off, whch implies the alternator is working (doesent it?).

 

Previously the light used to go out after an intial rev to 3krpm just to kick start it. Anyone know anything about alternators.

 

 

[Chris W]

Is the replacement alternator exactly the same as regards wiring connections, or did you have to make a judgement as to where the wires went? Which ECU do you have/engine variant/age?

 

Chris

 

2003 1.8K SV 140hp see it here

[julians]

The new alternator is not exactly the same as the old one.

 

The new one has two posts one marked B+ and one marked W. The old alternator just had two connections, but I'm not sure how they were marked (it was quite old and knackered) .

 

I've got two 'wires' the connect to the alternator, the first wire is actually a bundle of about 4 wires joined into one connector (This has always been like this) and is currently connected to B+. The second wire is just one wire and is going to W.

 

Like I say , at the moment the battery appears to be charging OK (+14v when engine running), its just that the light on the dash doesent go out. Could it be that there is another connection on the new alternator that I've missed which the dash light should be connected to, which at the moment is connected to B+ via the bundle of wires.

 

This is on a zetec with a DTA ecu in a 96 supersprint chassis.

[rj]

The point marked "W" is an output for a rev counter on a Diesel

 

"B+" is battery + strangely enough, four wires to take the current

 

and the one used for the light will be marked "D+"; that's the one you should ude.

 

On some of the very later cars the "D+" no longer exists and will be replaced by "DFA" which will be a load sensitive output for the ECU, haven't seen that in a se7en yet.

 

 

/rj

[julians]

Thanks for that, there must be another terminal on the alternator then that I missed when putting it in, will go and have another look at it.

 

 

[Chris W]

I agree with RJ. There should be at least 3 connections.....

 

....main battery connection (B+), charge lamp (brown/yellow) to D+ and a white/red which goes to the ECU for regulation control.

 

Chris

 

2003 1.8K SV 140hp see it here

[julians]

Thanks guys, sorted it now. There was a small spade connector which the lamp wire should be connected to.

 

There are still only two connections though. Remember this chassis (and hence wiring loom presumably) was originally designed for a carbed cross flow, so there is no wire for ecu controlled regulation.

 

All seems OK now. 14V with engine running ( as before) and no light on dash. I presume that it was still charging the battery before. Wierd, I thought that alts needed an excite current to start them off, I guess me connecting the lamp to the W connection must have provided that excite current via another means.

 

 

[rj]

Julians,

 

 

Nope, the W is only an output wich as far as I remember is directly from the coils, before the diodes, and hence an AC signal that indicates your engines RPM.

 

If your alternator works without the , I'd expect the reason to be that the manufacturer has installed a dummy resistor so that the alternater will work in a car with a LED charge lamp.

 

The DFA output will probably only be in a tintop produced after y2k

 

Anyway, now it works, and we all are happy, aren't we 🤔

 

 

 

/rj