Wahlnutz

I'm a wiring in 12v LED lights into my Lexus. I am using two add-a-curcuits for the positive wire. I am running of the Gauge 10amp fuse and the turn 7.5amp fuse. When I add the add-a-curcuits the old items running off those fuses won't work and the lights do work. When I go back to just the single fuse everything is fine again. I don't know what the problem could be. Any ideas? Thanks!