I took the pics of my added 'redundant' wires today. The first picture, you can see the second lead to the alternator. The wire to the right of the picture in Pic 1 is the factory wire. It's either a #6 gauge or #4 gauge lead. It leads to the battery, and hooks into one of the positive battery cables. There is a second either #6 or #4 gauge cable that leads from the battery to the fuse block under the hood, in front of the windshield. I really don't like this setup. I made the redundant lead feed directly to the fuse block. It is the same size as the factory lead, or larger. This effectively doubles the amp carrying capacity to both the battery, and the power center of the vehicle. The alternator is rated at 140 amps, but the lead from the alternator to the battery isn't designed to carry that load for more than a few minutes. It's more realistically designed to handle about 80 amps full time. The second lead allows for a full 160 amp capability full time. Pic 2 is how it looks going into the power center with the cover on. Pic 3 is how it's connected to the power center.
Pic 4 is of the redundant ground as it's hooked to the engine. You can see the yellow cap on the terminal on the left. It's hooked to the bolt above the water neck. If you look to the right, you can see the negative battery cable, and the lead attached to it leading from the block to the body. I replaced the OEM cables with factory replacements because they were 20 years old, and pretty corroded. Apparently GM has found the OEM units not sturdy enough, so the factory replacement cable is one gauge heavier than stock. The original was a #4 gauge, and the replacement was a #2 gauge. The factory lead from the block to the frame is a #8 gauge, and can handle about 40 amps. Automotive companies started adding these leads for a better ground when they found that just running a ground to the block wasn't enough. I added a #10 gauge lead to the same terminal as the factory lead, for another 30 amps of current flow. Pic 5 is of the terminal that the grounds are hooked to on the body. As you can see, several items are grounded to this terminal. The biggest ground on that terminal is the factory ground lead that hooks to the battery cable. the two with yellow caps are redundant grounds I have hooked to that terminal. The better ground you have, the less strain on the alternator.
It seems that something in the electrical system wants to put a drain on the system whenever the vehicle is running after the vehicle gets over 100k-150k miles on it. This setup overcomes that drain no matter what.