Okay, so I've been following multiple threads for awhile on aux battery installation and I'm lost now, expecially looking under the hood and now have some questions. Is my truck already setup for dual batteries? It seems all I am missing are the positive and negative cables for the aux battery on the driver's side. There is a red wire running from the battery to a fusible link on the firewall, which in turn runs along the entire firewall into the big black electrical panel on the drivers side. Also notable are two sets of coiled red wired, one is taped to the wiring harness below the master cylinder and another is coiled up and tucked along the side of the electrical panel. Here are my findings: Please note, I have no clue what the coiled red wires are for; thus me asking the experts here. Red wire coiled up under master cylinder to wiring harness: Fusible Link with battery cabling running along firewall to electrical panel on driver's side: Dual battery cables one to the starter (guessing) and one to the fusible link: Empty battery tray, driver's side behind headlight: If you look closely, you can see the coiled red wired below the master cylinder and the other on the right side of the black box. Coiled red wire along side driver's fender next to electrical panel: So, my question is: What do I need to get the dual battery setup installed in this 2009 GMC 2500HD 6.0L Crew Cab? Thanks for your help!