Alternator not charging again - ideas?

[DodgeRover]

My replacement alternator on the van has failed after about 8000 miles, it was a warranty replacement for another new one which also stopped charging after about the same mileage.

Charge warning light is on, it will flicker and go dimmer at sustained higher revs but won't go off, belt is suitably tensioned, anybody got any ideas other than poor work when it was rebuilt?

It's on a 2l pinto in a transit so very little electrickery to go wrong.

[scaryoldcortina]

It's probably the cable between the alt and battery that is failing.

[Rocket88]

Have you tested to see if it's charging?

[steveo3002]

youtube has some good videos , maybe try a new regulator /brush pack  and check the wire is good

[DodgeRover]

Have you tested to see if it's charging?

Voltage was around 12.4v dropped slightly with lights on. It was the same with the engine switched off.

 

It's probably the cable between the alt and battery that is failing.

I'll try replacing it carefully with a jump lead in the morning. Would bad connections or high resistance on this wire mean it doesn't see the correct battery voltage and hence fails to charge?

[scaryoldcortina]

Kind of. High resistance in the wire limits the amount of charge the alt can supply for a given voltage (Ohm's Law). A broken wire won't let it charge at all and often leads to a fried alternator, it's the same as running with no battery.

[castros_bro]

Is your meter a modern digital one?

 

Engine off and measure voltage at battery terminal.

 

Engine on measure voltage at battery terminals (not on the battery clamps)

                 Measure voltage  between big electrical terminal (not the end of the cable)  on alternator and alternator casing

                 measure voltage between big electrical terminal on alternator and the +ve battery terminal

                 measure voltage between -ve battery terminal and alternator casing.

 

Post the answers here for further diagnosis.

[Guest Hooli]

When your playing with jump leads also try earthing the body of the alternator to the engine block/bodyshell.

 

I went through three alternators on a Manta till I realised the fault was the earth lead from the alternator to the block.

[cobblers]

I wrote a long post but basically it boiled down to what castro said, with the addition of doing the same but with the headlights and blowers on full to put a load on the system.

[PiperCub]

As above for testing voltages but also as Hooli says, check the earth straps between battery & body and between engine & body. The former often suffers from corrosion (high resistance) at the body end and the latter is often pretty hidden away and gets broken or unbolted and not put back.

[sheffcortinacentre]

Ford alts of that age must have a good earth between alt body/mount/eng/battery.

Also make sure the ign light wire is good as if the light doesn't work it won't charge,it gets a feed from the ign swt (red or black) through dash light to the (blue wire)alt.

Check the small wire to the pos+ battery terminal is good too.

[Junkman]

It's so easy on Rover P6es.

 

- If your fusebox stinks of Amperes and is smoldering and goes on fire a lot, your alternator is good.

 

- If your fusebox doesn't smell and is like new, your alternator is fucked.