Auxiliary battery harness question

[B_derK20]

On this diagram (from another forum member) are the two batteries connected on the positive sides or is the aux battery totally independent of the primary? The diesel K20 I once had just had a cable linking the positive terminals but this gas motor truck is either missing that cable or it wasn't that way from GM. Can I run a cable like the diesel trucks or will that defeat the purpose of the wiring harness that's already there?

Thanks

[willett]

Looks to me like the aux batt is isolated unless the ign is energized.

The idea being that you can draw off the aux batt until it dies and then start the truck off of your untapped starting battery. One the truck is running your aux batt will recharge.