I replaced the starter relay on my 2007 2.7 dodge charger and it still won't start

Your saying the starter motor won't crank the engine? Does the battery have a full charge, battery connections all good? Have you checked voltage circuits at the starter itself? Usually two voltage circuits, one comes from the battery, hot all the time. The other goes hot with key in the crank position. That circuit voltage or ground is wired through the neutral or clutch switch, depending which tranny you have. Any testing at starter motor be sure tranny is in park or neutral and the parking brake is set. I haven't looked at your wiring diagram, yet.

Did you check voltage and ground circuits for the relay?

What about security system, where applicable?

Well you need to go here www.bbbind.com for free wiring diagrams , an then go to youtube an watch a few different videos on starter system trouble shooting .An voltage drop testing an basic electrical system testing . Then you need a DVOM - digital volt ohm meter , an do some testing . rather then having people on here tell you it could be this or that , you have to test . Oh yea check out how to test a relay .