In order not to void the warranty, should I always do mantainance (filters, engine oil, brake, ...) in a ford dealer? Do I have to stick to motorcraft band for the parts?[/QUOTE
Keep all your reciepts and records. If you have a failure and the dealer can connect it to lack of maintenance you can get stuck holding the bag. I work at a dealership and encourage owners to at least check in every now and then for computer updates, recalls and anything else that may be common on your car. It is alot easier to present your case when you have visited a dealer every now and then. Dealers in the past had write off accounts that they could dig into to help ease the expense to a customer that got seated with a bill they did not agree with. The store I worked at would sometimes help especially if the customer had frequented the dealership.
Ditto;Look at the contract as most 3rd party warranties can decline for ANY vehicle modifications as well, even if they are not related to the problem. The contract will tell you what is and isn't covered, these 3rd party warranty companies are perticularly good at one thing... Taking your money and giving you NOTHING. I have seen many people get burned because they had an exhaust system or an intake system and their coverage was declined, though the modifications did not cause the problem.