Alternator problems....help please!

Hiya,

I changed my alternator as it was starting to squeak, the replacement didn't charge the battery leaving me on the side of the road waiting for a recovery.  A jump start got it back on the drive from the truck but still no charge.

I changed the alternator for another, it came from Roy Blackman in Kent and is New Old Stock, but this one isn't working either.  The orginal one was refitted to see and won't put in more than 12v now.  The NOS one is back on the car, the battery has been tested on another car and is fine.  All fuses in the box are intact and I don't know where to look next.

Any help would be greatly appreciated.

Thanks

Check the large earth strap from the neg terminal to the chassis.

Also the large red wire from the alternator may be changing.

Strap seems ok.  When I put the multi meter on the alternator and the + terminal I get a 12v reading.  Is that right? Shouldn't it be 14?  I have a push in plug type alternator and the only red wire is the small one between it and the block.  That also gives a 12v reading.  

Sorry but I'm not that good at electrics!

Turns out alternator isn't producing a charge.  What a pain eh?

The red wire is the one from the alt to the battery + terminal unplug the alt and take the other end off the battery and do an ohms check. It shouldn't be more than 1 ohm at most.

The earth strap can look ok but may not be ok. You can do an ohms check from the alternator bracket to the neg terminal of the battery with the + terminal of the battery disconnected.

See how that goes but you may have 2 duff alternators in which case it's usually the voltage regulator on it.

Hope that helps

If the car is able to start (from a charged battery) then the earth strap is not the issue.

It sounds like the blue wire to the alternator is disconnected - does the battery light come on before starting (key turned to 2nd position), then once the car's started and revved up, it goes out?

If the light doesn't come on, the wire's not connected (or there's an internal fault on the alternator).

paul_c said

It sounds like the blue wire to the alternator is disconnected

You are spot on.  Turns out to be a blue wire issue.  Apparently it was a common fault so I am told.  I've had the blue connector of the plug cut off and a regular spade put in it's place.  Problem sorted.  Now pushing out 13v when running!

Thanks to everyone who posted, it was very helpful.  

 

Unless that voltage goes up you still have a problem.  :?

And Paul, as for the earth strap, I agree to a point, but it is possible to have a bad earth and start the car especially with a fresh battery. One impacts on the other wouldnt you say?