I want to improve the link between "Purchasing" and my Plant

Despite the fact I have approx 7-1/2 years experience in Purchasing I consider myself new to the world of "Procurement". Until May last year my only Purchasing experience was with a small single site distribution organisation where I managed a two man team. I now work for a global multi site tier one Automotive component manufacturer and to say this was a step up in my carrier is an understatement. I often find myself overwhelmed, especially as I am the only Buyer (responsible for both Mass Production Direct Purchasing as well as Overhead Indirect Purchasing) on site reporting to a Group centralised Corporate department. Anyway, I find especially in my Indirect Purchasing responsibilities the general relationship between the Plant and the Purchasing function to be very broken. The previous Buyer before me wasn't very popular with the rest of the plant and I also feel cultural differences between the plant and the central group aren't helping matters. I am finding a lot of misconceptions about how Purchasing is only concerned with price and want to slow down processes and create process blocks for the sake of taking control. After discussions with the Plant General Manager we've agreed that it might be good for me to give a presentation to some key internal stakeholders. I want to them understand better what is I do and how I feel they should work with me to help me give them a better service, they are my customers after all! I want to help them understand the importance of contract and KPI management and Early Buyer Involvement! Can anyone give me any good pointers to focus on? Are there any guidelines or publications I could that specifically address this topic that are readily available online?