hsfdchief200

Thank you so much for the info and pictures! Getting the 84906880 harness and auxiliary battery fuse block would definitely be the easiest and cleanest method to do this. I guess my only remaining question is the underhood junction/fuse block (X50A on the diagrams) that's on the driver's side right beside the spot where an auxiliary battery goes. Currently, in the single battery gas setup, there is a wire running from the battery on the passenger side around the firewall to this junction block. It's fused on top of the battery at 175A. It only goes to this junction block and doesn't have any other branches from the harness. From everything I can tell from parts pictures, the 84906880 replaces this wire with these differences: it's fused at the main battery at 400A, fused at the other end at the auxiliary battery at 400A, and has a short dog leg coming off the auxiliary cable terminal to loop over to this junction block. With the 400A fuses on both end of the 84906880 harness, that junction block just went from 175A to 400A circuit protection without any other changes, which doesn't seem very good to me. I can't find an upfitter wiring diagram that shows how this is handled at the X50A junction block in a single alternator diesel truck. It only shows this junction block on the dual alternator diagram, even though I know it's there in both applications. In this situation, it might be best to determine an appropriate cable gauge to use to go between the batteries and just run my own custom battery cable with a 400A fuse and leave the factory junction block wire and 175A circuit protection in place for that junction block. I hate to start disturbing very much of the factory wiring if I can help it. Basically, I need to get two 400A mega fuses, appropriate cable size and terminal ends, auxiliary fuse block to go on top of the new battery and just leave everything else as-is. Does this sound correct?

I looked back in the upfitter guide and found diagrams, but they don't show the wire size (at least that I can find). Could I simply order the main battery cable for the diesel and use it for the run between the two? I found the part for a diesel, dual batteries, single alternator - 84906880 ( 2020-2023 GM Battery Positive Cable 84906880 | GMPartsDirect.com ). It looks like it connects at the driver's side battery, has a small pigtail to connect to the driver's side junction block, then a long run to route over the firewall and connect to the passenger side battery. Would it be feasible to just install this?

2 gauge battery cable is rated for more than 65 (210 outside engine comp, 178 in engine comp per one vendor I've been working with), but it definitely isn't rated for the high max current this winch could draw at full load. That was also surprising to me when I unboxed it, but it's hardwired this way straight from Warn. They also say to wire it directly to the battery with no fuse or switch, which goes against every fiber of my being, but that's a whole separate topic. I guess how they get away with the 2 gauge is the short run and limited run time of the high amperage. Wiringproducts.com shows a 2 gauge battery cable capable of 300A for a 4.9 ft. run with 2% voltage drop.

Do you know what size wire and fuse the diesels use for that run between the batteries or where I could look to find that info? I don't know of anyone in my immediate circle who has this version truck with a diesel. I just checked the fuse block on top of the main battery. There are no unused fuses. It has a 250 which goes to the alternator, a 175 which goes to the fuse block on the driver's side, a 400 which goes to the starter, and two 60s which have wires going into a harness below the battery.

That is correct.

I have a Warn 16.5ti-s winch that I'm installing on our fire dept's 2023 3500HD with the 6.6 gas. The winch can draw up to a max of 507 amps, per Warn. This truck came with the snow plow prep package, so it already has the 220 amp alternator but only a single battery. I came across some older posts about adding a second battery that was isolated, but I haven't found an answer on my scenario. My preference is not to have the second battery isolated but instead have it wired in parallel like I understand the diesels to be. Is there a problem wiring this in parallel and simply running positive to positive and negative to negative between the two batteries? If it's ok to do, what gauge cable should I use? The winch has 2 gauge cable going to it. The truck will also have a 2 gauge cable running back to a junction block on the flatbed to power the electric starter on the pump's Honda engine and for the electric rewind motor for the hose reel (50A fuse for that motor). My main reason for not really wanting them isolated is so that the ever-rotating crews of people to use the truck will know for sure if one or both batteries start getting low if wired in parallel, as starting will become apparently weaker. But if they are isolated, that auxiliary winch battery could be getting low without anyone realizing it, and I don't want to be in a situation of needing the winch and having a dead or near-dead auxiliary battery. NOTE: As bad as it is, I have to engineer for the lowest common denominator. I had even thought about a dual battery voltmeter installed in the cab, but that wouldn't get monitored (and most of the guys coming through nowadays have very little mechanical knowledge as it relates to vehicles, so it wouldn't mean anything to them). So I want as simple of a setup as can be safely done. So I guess my questions are: -Can a parallel dual battery install be done on this gas truck for a winch install? (I realize I need 2 new equal batteries to install at the same time - that's no issue) -What gauge battery cable to run between the batteries? -Should the winch be connected to the main battery or the second one (or does it even matter being in parallel)? -Is there anything else to be done to the wiring to prevent any overcurrent or overcharging issues?