Battery setup with three wires: two negative and one positive

In the learn something new every day category. 
This battery has three wires: there are two in the wire harness that go to the battery switch.  One with the fuse for the positive, one white for the negative.
But: what is the extra white cable for?  I'm assuming it is another negative cable....but, where does it go and what does it do?
This trailer is a 2017, no solar port or solar.
I did find a reference to the "three cable" setup in the thread below from 2014.  The thread seems to be missing some comments, but with an old thread, that is probably normal.
In the photo, the mystery cable seems to be the one in the top circle.
And, if you insist/need to remove your battery, do yourself a big favor and take a picture of the wiring before doing so!

2017 Outback
Towed by 2014 Touareg TDi


  • Grumpy_GGrumpy_G Member Posts: 445
    Don't assume, confirm with an ohm meter that the second white wire connects to the trailer frame. It is likely that the single wire goes to the frame while the one in the plastic loom goes inside the trailer.
  • webers3webers3 Member Posts: 404
    edited April 2
    I have 2017 320, it has 2 white wires to the negative side of the battery but it also has solar port, that's where one white wire goes to. Without solar port I am puzzled, definitively no solar port?
    2017 T@B 320S   2019 Jeep Cherokee - Southern Connecticut
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