I have done the search thing on this issue for about a week now and am still confused about what exactly to do. I am installing a Prodigy in my truck and have also purchased the GM brake harness 3015-P to go with it. I understand that this needs to be plugged into the under dash "convienence centre", top row, second from the left slot. The other end simply plugs into the Prodigy. Where I am confused is the use of a fuse or auto-reset circuit breaker. Tekonsha's instructions show what appears to be an in-line auto-reset circuit breaker. How is this different from the guys that are just putting a 40 amp fuse in stud #1 and a 30 amp fuse in stud #2 in their underhood fuse box? There still seems to be a lot of confusion in the other threads I searched about whether or not these fuses need to be used or not? I.E. dual batteries/wanting to charge trailer batteries while in tow.