Hi, This is my first attempt to run a Adwords for my Auto Lighting Accessories store. Should I consider the broad keywords like "projector headlights", "Euro Tail Lights" or narrow keywords like "accord halo projector headlights", "03 BMW E36 Euro Tail lights"? Thanks,
Why don't you try them all and see what converts instead of asking us, people who more than likely know nothing about your business?
definatly try all options and conclude from that... When selling accesories for a machine (i do this for motorbikes, you cars) definatly have a section (adgroup) where you focus on brand name + item and brand model + item and brand name + model + item. If you're smart you can probably even use dynamic ads with keyword insertion so you don't have to write 4000 ads for 4000 products. then start studying keyword performance
The best part of this business is hopefully your niche knowledge... and you should sell on that. no one is going to know about "03 BMW E36 Euro Tail lights" like you do. What I would recommend is for you to dump your whole inventory into the system. and let it run for a while. Have you read "the long tail" book http://www.thelongtail.com/
I have an automotive client I'm working with right now and I can confirm the pay per click world is expensive for all automotive products. With that said, you need to spend a good bit of time on your ads and website (landing page). Now, my experience is in automotive clutches. I have found that being more specific will get you better CTR and conversion rate. I still recommend you include general and specific keywords, but you must have the specific ones. Apparently, the automotive gear heads like to search using very specific terms (make, model, part manufacturer, specs, etc.). Spend the time putting them in. Use the Google AdWords Editor to save time.