Hi. I purchased a new genuine Cosworth alternator from eBay. I have put it into the car however it won’t charge! The engine is in a mk3 fiesta. Battery relocated too the boot. Thick cable runs from the batt to the starter then from the start to the alternator. I then have the exciter wire connected to “Off the top of my head “ D+ ? Turn the ignition on and the battery light comes on on the dash. And exciter wire has 12v at it. Start the engine and nothing! Battery light stays on and alternator is giving 0v. Any ideas ? Or is it just a faulty alternator ? Thanks.

 

It sounds like it, it could be the regulator though.

I am hoping you did not pay "Cosworth tax" for it?

Martin

 

Hi no got it for around £80. So wasn’t bad. However I removed the alternator last night and tested it and the alternator is working! However I believe because I am using fiesta clocks the battery light is the wrong wattage and causing incorrect power to the exciter wire. So will need to add a resistor

 

Ah ok, note that 3DR and 2WD are different in terms of output, but this is going off at a tangent and is immaterial.

I doubt it, I suspect they are all the same, like 3W IIRC.

Adding a resistor will of course reduce the power.

Is the light bright?

Martin

 

the alternator is charging, but the light needs to go out, that's where the fault is

between the alternator and the dash

 

It won't be, as there will be a potential difference for the light to operate.

The OP could be right in that someone has changed the bulb for an incorrect one, but I am assuming it was working ok before the engine swap?

Martin

 

but if the light is on it means the alternator isn't doing it's job

that would be the easiest thing to look at first of all wouldn't you say?

 

The wire for the light is Earth when no power comes from the alternator, other side of light goes to switched live, then when alternator is providing power the wire becomes live thus the light goes out, this needs to happen for the alternator to work. Also make sure the engine has a really good earth strap or add another and make sure the earth is really clean.

 

Correct, but previously you said it was charging, which is what I was referring to.

Martin

 

i see how it could be interpreted like that