charging issues

[timoteo]

Hi Everyone... just after some suggestions... my 75 cdti has charging issues... well it doesn't charge - no voltage above battery volts. Battery light on. I have changed the alternator for a refurbished one. Done voltage drop tests on the postive post to battery and casing to battery - all good. Seems fine there. Fuses fine - one in under glove box.

There was a post on here a while back saying that wiring can fray behind offside headlamp. What would be the symptoms for that? I do have voltage on both pins in plug on back of alternator with the car running... battery voltage in one and about one volt less on the other pin... (the one going to the dash?). The headlight wiring caught my attention as a couple of MOTs ago the garage couldn't figure out why the horn doesn't work (I never use it) and they installed a new one and as I understand it the wiring for the alternator goes out the same way as the horn loom.... could it be the culprit? I don't want to take the car apart un necessarily especially as the car is beginning to get ultimatums from wife... you spend far too much money and time on that car etc etc.. I suppose it could be the 'new' alternator' but that really would be NAUGHTY WORD-NAUGHTY WORD-NAUGHTY WORD-'s law and I'm not willing to get another to try. Although the light only just came on it has been showing alternator symptoms for a while - dimming headlghts on acceleration. The old alternator had no continuity between the slip rings so I would assume that it was a gonner as the rotor needs continuity. So not sure why still have issues. Any ideas?

[grivas]

Originally Posted by timoteo

Hi Everyone... just after some suggestions... my 75 cdti has charging issues... well it doesn't charge - no voltage above battery volts. Battery light on. I have changed the alternator for a refurbished one. Done voltage drop tests on the postive post to battery and casing to battery - all good. Seems fine there. Fuses fine - one in under glove box.

There was a post on here a while back saying that wiring can fray behind offside headlamp. What would be the symptoms for that? I do have voltage on both pins in plug on back of alternator with the car running... battery voltage in one and about one volt less on the other pin... (the one going to the dash?). The headlight wiring caught my attention as a couple of MOTs ago the garage couldn't figure out why the horn doesn't work (I never use it) and they installed a new one and as I understand it the wiring for the alternator goes out the same way as the horn loom.... could it be the culprit? I don't want to take the car apart un necessarily especially as the car is beginning to get ultimatums from wife... you spend far too much money and time on that car etc etc.. I suppose it could be the 'new' alternator' but that really would be NAUGHTY WORD-NAUGHTY WORD-NAUGHTY WORD-'s law and I'm not willing to get another to try. Although the light only just came on it has been showing alternator symptoms for a while - dimming headlghts on acceleration. The old alternator had no continuity between the slip rings so I would assume that it was a gonner as the rotor needs continuity. So not sure why still have issues. Any ideas?

Hi, can you start the car with the replacement alternator connected battery connected and can you read the voltage across the battery terminals as the car is running.?

[Mike Noc]

Originally Posted by timoteo

There was a post on here a while back saying that wiring can fray behind offside headlamp. What would be the symptoms for that?

Funnily enough the symptoms for a wiring fault from the alternator plug back are that the alternator light stays on and the battery doesn't get charged.

[COLVERT]

Quote.---Done voltage drop tests on the positive post to battery and casing to battery.

I've tried but I don't understand this Quote--


The alternator is connected straight to the battery so no need to think about the other wires you mention.

Everything points to a duff alternator.---( It does happen, I know from personal experience. )

[dave lincs]

Check you have 12v on the main wire that comes from starter motor to alternator I've seen this badly corroded before

[timoteo]

Originally Posted by grivas

Hi, can you start the car with the replacement alternator connected battery connected and can you read the voltage across the battery terminals as the car is running.?

yes does start but voltage stays at 11. something on the battery - I know the battery needs charging up.

[timoteo]

Originally Posted by Mike Noc

Funnily enough the symptoms for a wiring fault from the alternator plug back are that the alternator light stays on and the battery doesn't get charged.

but would I still get voltage at this plug if it were grounding somewhere else?

[timoteo]

testing from positive on alternator to positive on battery shouldn't and doesn't mark more than .2 volts lost through resistance on cable. Likewise negative on battery to casing on alternator. If it did it would show current loss in cable.


There are 3 circuits to think about - ecu to brushes and rotor which needs power for the alternator to produce current, dash light which will be cut off when the alternator produces current... these are both on the multiplug, and stator to positive on battery via starter motor.

Originally Posted by COLVERT

Quote.---Done voltage drop tests on the positive post to battery and casing to battery.

I've tried but I don't understand this Quote--


The alternator is connected straight to the battery so no need to think about the other wires you mention.

Everything points to a duff alternator.---( It does happen, I know from personal experience. )

[COLVERT]

Forget the ECU.--If you had just an alternator and a battery and joined them together and applied a drive to the alternator the battery would take a charge.--All the regulating electronics are built into the end of the alternator.---( Diodes and charge regulator. )

[COLVERT]

Two things.---If all your electrical connections are good and you still have no charge at the battery your alternator is DEAD.---