I don't know for sure which relay it switches, but I am assuming that it switches between the two fuel pump relays depending on condition. I installed the $25 salvage yard alternator, problem solved! I am going to go back and get another one and keep it for a spare, probably take it to a reputable electrics shop and have it rebuilt, install it and keep the old one for a spare. With a Trooper running up on 20 years old, I could probably never have enough spare parts<img src="/forums/images/graemlins/notooth.gif" alt="" />! The fellows at Napa will not be too pleased with me. It is important to note that with the engine relay removed the battery is not charging, at least as far as I can tell. I assume that part of the function of the engine relay is to switch from battery power to alternator power. If you are curious about this, search the archives, there is a TON of great information about this specific problem. Thanks to the board for all the great info. I think this is one of the best BBS's out there! Thanks to everybody!!