As long as you wire it as per the diagram you will be fine.

 

If you've got it apart it's not hard to check. With the ignition off use a multimeter to check for continuity between the forward pins then the back ones. If they are common they will have close to 0 ohm resistance. You can then test for continuity to the -ve terminal of the battery. If you find it then it is common earth. If not, you would then turn the ignition on and test for 12V on one side of each injector. If you find it, that's a common, always on, +ve. Hence the earth is switch as someone suggested.