Hi, 

I recently changed my alternator as the pulley went bad. I bought a remanufactured one but it's making whining noise so I told the seller and they offered me a refund. 

I am now looking for used alternator from the ebay and come across two different part numbers. One is 1685794 and the other one is AV6N-10300-HA . 

None of the sellers can tell me if those are compatible or not so it would be great if anyone can help me with it. When I put those part numbers on google and some alternators are compatible with both of the part numbers. 

https://www.buycarparts.co.uk/valeo/16165840 This one is saying that the alternator is compatible with both part numbers.

Is that mean I can go with either one of them? Thank you. 

We don’t know which engine you have. In my experience there are often many variations on alternators which are interchangeable. Eg different makes that Ford used in different years and the connectors being in different positions and different amp outputs. So, often an alternator can be different but still fit.   Of course make sure any connector plugs are right shape and right number of pins. I know that does not make it easy, but if it looks different it does not necessarily mean it’s wrong

46 minutes ago, isetta said:

We don’t know which engine you have. In my experience there are often many variations on alternators which are interchangeable. Eg different makes that Ford used in different years and the connectors being in different positions and different amp outputs. So, often an alternator can be different but still fit.   Of course make sure any connector plugs are right shape and right number of pins. I know that does not make it easy, but if it looks different it does not necessarily mean it’s wrong

I have 1.4 petrol 2009 fiesta. SPJA engine I think. I compared photos of the current one and the one on eBay and they seem to be the same so fingers crossed 🙂 

The part numbers you have are 2 different systems.  The 7 digit number is the finis number which is used to search the ford parts catalogue.  The number starting AV is a more specific part number that can be used to denote minor differences in superceded parts for example.  So it's possible that both numbers are for just one part.  You'll also find aftermarket parts are often compatible with many different part numbers.

As Isetta says, as long as the alternator looks the same and has the same ratings, you should be able to swap them without issue.