_GM Fuses

Fusible Links

An electrical fusible link is a type of electrical fuse that is constructed simply with a short piece of wire typically four American wire gauge sizes smaller than the wire that is being protected. For example, an AWG 16 fusible link might be used to protect AWG 12 wiring. Electrical fusible links are common in high-current automotive applications. The wire in an electrical fusible link is encased in high-temperature fire-resistant insulation to reduce hazards when the wire melts.

What you need is a fusible link that is 5.0 square mm in cross section, rated for 50 amps, about 6 inches long, unwrapped in free air, not enclosed within a harness or convoluted tubing, and incorporated into your 6 guage charging wire as near to the battery as feasible. In general, fusible links are sized 2 guage sizes less than the parent wire they protect... so two wire guage sizes smaller than 6 guage would be 10 guage. And 10 guage is equivalent to 5.0 mm sq. For what it's worth, GM uses 5.0 mm sq. fusible links on their factory auxiliary battery option for the charging wire. Two, actually. One between the battery and the relay, and the other between the relay and the starter. In additon, GM has a 40 amp Mega fuse protecting the loads from the Auxiliary battery. Fusible links function differently than many fuses. It should be of interest to you why the factory choses fusible links for the main high current starting and charging circuits, versus fuses and circuit breakers elsewhere. Fuses of all types... Mini, Maxi, Mega, fusible links, and circuit breakers offer the same function, protecting against damage from electrical overcurrents, shorts, etc... but even though they do the same thing, they are obviously not all the same. Therefore, the logic that an inline fuse would be just as good is somewhat circumspect. I would use a fusible link, since that is what every car I've ever owned and worked on has used from the factory for the circuit you are trying to protect. I don't know why the OEMs use fusible links, and since I'm not an electrical engineer, I'm not going to assume that an inline fuse would be just as good, because every production and professional (such as emergency vehicles) installation I've seen uses fusible links. When searching online, I found that fusible links are used in battery charging and starting circuits due to their temporary high currant handling... they allow high amperage to flow for starting for example, where a fuse would blow within a certain number of milliseconds or seconds (depending on type of fuse sloblo etc), and a cirucit breaker would trip, cool, engage again, trip, and continue that cycle. A fusible link on the other hand, works for protecting from catastrophic damage from a dead short that isn't consuming the current by turning a motor, but is instead just generating heat. Thus the link melts apart, end of current flow. That is why the fusible link needs to remain free in air, unwrapped and unbundled with any other harness. A sloblo fuse might still blo before your truck gets started, which would encouage the operator to use a higher value fuse... which then may not blow when required for protection. It seems easiest and safest to replicate what the professional electrical engineers already worked out for the vehicle, rather than try to guess what will work. Capitalize on the engineering you already paid for with the price of the truck. Don't take my or anyone elses advise on the internet too seriously, without first looking at it through the prism of what was professionally designed not only for your vehicle... but is found in similar patterns thoughout most vehicles manufactured.