In addition to fuses, some circuits use fusible links to protect the wiring. Like fused, fusible links are one time protection devices that will melt and create an open circuit.
Not all fusible link open circuits can be detected by observation. Always inspect that there is battery voltage past the fusible link to verify continuity.
Fusible links are used instead of a fuse in wiring circuits that are not normally fused, such as the ignition circuit. Each fusible link is four wire gage sizes smaller than the cable it is designed to protect. Links are marked on the insulation with wire gage size because the heavy insulation makes the link appear to be a heavier gage than it actually is. The same wire size fusible link must be used when replacing an open fusible link.
See Figure 1
To replace a damaged fusible link, disconnect the negative battery cable, cut the link off beyond the splice and replace with a repair link. When connecting the repair link, strip the wire and use staking type pliers to crimp the splice securely in two places.