hi,battery light remaining on when engine running,does anyone know price of either new or used alternator...my car is 52 plate octavia 1.9 sdi

First I'd check the following:

Check the 2-pin connector is correctly plugged into the alternator.

Check the fuses on the battery.

Check the main cables are secure.

Check the drivebelt.

It may be the brushes that have gone. IIRC, you can't just replace the brushes - you have to replace the brush/regulator module. If it is brushes, then replacing the module is a better option than a second hand alternator, as unless you measure the brush length in the second hand alternator, you just don't know how long it will last.

That usually indicates a loose drivebelt, or an over or under-charging alternator.

The first case is obvious (check belt tightness, and replace auto tensioner if necessary). In the second case, as RWB says, the suspect is usually the regulator (aka control box).

thanks to rwb&ken..my guess it,s the alt .new tensioner 6months ago,is it a job i could do myself?..is it a c a v or a bosch ? been looking online at alternators they are not cheap!..brush assembly can,t be that expensive can it???..

I'd think more likely alternator too then. Unfortunately it's quite common for which alternator was fitted to a specific car to depend on which maker last delivered a batch of that specific generating capacity, so we probably can't help you there.

hi, sorted the alternator myself,was quoted £250.for new alternator,but took it off,took out old regulator(brushes were well worn)got new part,hey presto, perfect ....total price £41.70....thanks to everyone for your advice.....