You know you shouldn't be playing with batteries in the dark. I'm an idiot. You would think I would've double triple checked the connections of my 2nd battery, but no I didn't and lo and behold I fried my 75amp fuse that powers the ignition/painless fuse block circuits. It took me a while to find the damn fuse because it's a bit hidden and well you know after 3 yrs you kind of forget all the wiring intricacies you pulled!! Anyway, I decided yesterday that it was time to get the 2nd battery isolator wired in because before I just made a cable set up with the welding quick disconnects to plug into the feed I had made for the rear winch. I didn't plug it in until the other day when I thought, let's see if it's getting charged(hadn't wired in the isolator) and that's when the 75 amp fuse blew, and I unplugged it forthwith and it has remained unplugged since today. So I get the 2nd battery isolator side all wired in(except for the power feed that has to go back into the cab and feed the required circuits) and bam the 225 amp breaker between the isolator and 2nd battery trips. Now I'm like what the hell is going on!! First off when it blew the 75 amp fuse I'm thinking, ok why have I been able to plug into the winch power cable and jump-start the truck before I added the 2nd battery with no issues, and so now why did it blow the 75 amp fuse? I couldn't figure out why and left it to I'll figure it out when I wire in the isolator, but it still bugged me, because nothing made sense. So after the 225 amp breaker trips and I unplug the quick disconnect I'm just staring at the battery wondering what the hell is going on!! And then I noticed on my negative battery post clamp there's a + sign stamped into it and I think that's weird why is there a + sign on the negative post? Then I look a the positive battery post clamp and there's a - sign stamped into the clamp. Geesh I think, how the hell didn't I see that before, well it was dark & getting colder and I definitely wasn't paying attention!! But yet still I'm like ok, so the clamps are off, but they're wired to ground and positive correctly(oh no they weren't in reality), so maybe the battery posts are just different on these batteries. Then I take another look and shit right there I had negative wires going to the positive post and the positive wires wired to the negative post. I was like you have to be kidding me. But since I didn't plug the battery cables into anything that night there were no sparks or indicators that I had the cables swapped. Anyway, a stupid move on my part and it just goes to show that you can't double check yourself enough even though you've been working on cars forever!! So in the end I had to rotate the 2nd battery so the cables would connect correctly and luckily I had enough slack to make that work without having to make new ground cables and plugged it in and it charges through the isolator and no fuses blown or breakers tripped. So again I need to get a cable to run back inside the cab to power whatever I can outside the ignition circuits, but to do that I need some more 1/0 cable which I'll order today and I did buy an 80 amp breaker to replace the 75 amp fuse cuz that fuse is a pain to pull out due to its location and well breakers are easy to reset vs digging around for a fuse and you don't need to carry around fuses.