Funkdoktor

Hey Guys, looking for a little help. I recently replaced the fuel pump on my 2003 tahoe. Aside from having to cut an access hole, it was relatively straight forward. However once I got done and closed everything back up, my fuel level indicator isn't working. I obviously put one on the pump. I guess my question is this: On the wiring harness their is 4 wires. A purple, a grey, and 2 black. I assumed that both black are both grounds, and it shouldn't matter which black I hook to which black. Ground is ground. Is this an accurate way of looking at it? I really don't want to go through the trouble of getting to that harness again if it doesn't matter which black wires were wired together. And lastly, what else could be causing that fuel level indicator to not work(besides a faulty indicator).. many many thanks in advance.