Thanks, I had forgotten that part of the instructions - harness is on order. But, the four to three wire adaptation is not spelled out in the above instructions. GM is providing a pin out and I have the electrical troubleshooting manual for the Isuzu so I should be able to figure it out.

One other thing, if you remove the 16g wires going to the fuse box under the hood, I’m not sure how well if would work to feed current back from the battery since it was not designed that way. I was going to take the new 4 gauge wire straight up to the battery and leave the two 16g wires connected as is. Any thoughts?