Ok here's the deal. I already know how to do this with my D90, but I had my D90 replaced and the new one I received doesn't seem to be working correctly. Here's what's going on. I want to have have my camera trigger the flash wirelessly, so I set my flash on remote. Then I go into my flash settings on my camera, I tell the built in flash to be a commander instead of TTL. Then I go to the next screen and tell the built in flash to be (--) which means it should be inactive. Then I tell my speedlight to be manual at say 1/4 power. I should be good to go. I open my pop up flash (without doing that it wont trigger the speedlight) and I dial in my settings. I focus, compose, then shoot and strangely enough, both flashes go off. The pop up shouldn't even go off with the (--) setting. My other D90 never had this issue but I'm thinking this one might be defective. Am I missing something?