Touring tailgate wiring

[e30-320i]

I have just finished fitting a replacment tailgate to my touring as mine was more rust than metal. But as i was splicing the wiring together i've noticed there are two brown wires which are both the same size so i'm unsure which wires are which.One appears to go to the wiper motor and the other looks like an earth.I have tried the wires both ways and everything works as it should but does it matter if i've got them the wrong way round and how can i tell .

[Brianmoooore]

All plain brown wires are earth wires.

[e30-320i]

Thankyou mister moooore