Installing a Kriss Technology modulator will do it. Mine were originally hooked up that way with the modulator, but I had them rewired to make the trunk lights flash like turn signals for what I think is better visibility, plus the trunk lights modulate--steady for a few seconds, then a few flashes, then repeat. (At least as I recall without going out and taking off the cover and looking at them all again.) I suspect more technically savvy board members will be able to tell you how to hook a wire in somewhere to just do what you're looking to do without all the modulation, though.