how can i tell if my alternator is faulty or my wiring?

4 days ago my battery light came on on the dash after about 15mins it went out again, on the way home from work it did the same again it is now on permanently the van starts ok and the battery still seems strong i put a multi meter on the battery and it measured about 12.5v i turned the lights on and it dropped to 12.25v and stayed at that and didnt drop any further. i pulled out the plug on the alternator started the engine and the light was out put the plug back in and the light came back on. any ideas??? my van is a vauxhall combo 1.7 diesel and is a 97 model
david hill, July 2005


done
your alternater reading of the battery should be reading 13.5v ive had the same problem mine started doing the same thing has yours with the batterie light.then it got worse clicking noises and lights not working properly etc! basicaly you may need a new alternater the way you can tell if its your alternater is after you have driven the van lift the bonnet and you will be able to smell fibres burnig in the alternater! it meens a new one !!!!!!!!!!!!

pike man, December 2006
1. Pulling the plug disconnects the alternator's charge sensor, therefore - no ignition light!
2. Is your fanbelt tight / clean / in good condition?
3. Is your wiring in good condition?
4. Are ALL the battery connections tight?
5. a: How old is the battery? (more than 18 Months - get it checked)
b: Is the battery a 'calcium' type? (Known to have intermittent problems after alternator faults)
There are other items, but eliminate the above first!

Tencon, September 2005
link Click here to see other fixes for Vauxhall Combo.