do they go straight into a mains plug or do they have a little power supply kinda box?
If they go straight into a mains plug then you only really have 1 option ( +ve and -ve) !
Can you open the plug and see if they are paired together in any way? If so then it maybe that the 4 leads are just 2 pairs. Often with little lights you only have a continuous wire that goes in a loop - out and back. One end +ve and the other -ve
If they have a little controller/power box then it will be more difficult as you may have some sort of communication wire or multi volt config in there.
Note the output voltage on the power supply (12v DC or similar)
If it's low voltage/current you might be able to try a combination of wire-to-wire until it works
As always when working with electricity BE CAREFUL and if you're not confident - get a pro to do it for you. Good luck!