If you do a search on the relay here in the forum you will find more than enough info. It is located on top of you engine in the middle by the fuel filter under the plastic cover that says something like 7.3 on it or so (mine is gone so I don't know). It is a fairly big relay, 2 big posts and 2 small ones. Get a buddy and a volt meter. One of the big posts will always have 12V against ground, find that one. The other big one should have 12V after the key is turned on. Check it when the truck is cold, it should stay on for about 30 to 45 seconds. If the other big post doesn't get 12V it is bad. They are a bit pricey so shop around before getting a new one.