Proposing to install a battery isolator switch, primarily for when working on the car and also for security purposes. The type with the removable red handle.

Question is, which of the 2 red wires behind the rear bulkhead do I break into? Is it the larger wire or the smaller wire?

The smaller wire goes into and returns from a plastic housing near the battery. Anyone know what this housing is for?

Pic below shows the housing.

[Linked Image]

Chris

2015 Plus 4 Silverlake Blue
(2014 3.7 Roadster Crystal Blue)
(2012 4/4 Sport Black)