l have a 807 2.2HDi and the auto lighting is faulty - l have been told by peugeot that the indicator arm has a faulty wire and needs to be replaced - cost approx £500 - for the unit. Does anybody know where l can get a 2nd hand cheap unit. Thanks

Firstly the unit should cost no more than £200 plus half an hour labour to fit it, & that is from Peugeot.
l would try another dealership & report this one to Peugeot UK as l think they r trying to fleece you.

Secondly, if u do buy a 2nd hand unit then u need to make sure that it is from a vehicle with EXACTLY the same equipment spec as yours & the same age, any slight difference & the unit will be a different model number & will not work correctly.
My experience of customers buying 2nd hand electrical parts is that they r always wrong, despite assurances by the person that sold them the item that it is the same, so they usually end up spending a lot more in the end.