Truck Aux input goes in and out...?

I'm not sure whats wrong. I know my speakers on my truck (10' Ram) work, and I know my iPhone works... so either my aux cord is broken, or my aux input is broken. If I mess with the wire by changing its tension into either the phone or the truck it works, but if I move it slightly it doesn't work at all... Is it most likely the input on the truck or the phone, any help would be great....