Where is the fusible link located?

Likely you have a blown "fusible link". These are located either near the battery + or the starter and can be difficult to locate.

Need vehicle information

Check the starter connections for a corroded/blown fusible link.Pull on the wires attached there and if one pulls apart easily,it's defective.

They use a fusible link at the battery.

Check fuses, check light switch and relays. This sounds like a no power issue so check fuses first. The light switch turns on or activatves relays which the power or voltabe to the lights .

https://s26.postimg.org/gukptsw7d/headlamps.jpg

Click on the link.
Usually on older vehicles, the headlamps don't use a fuse, but, fusible link, as shown in the diagram. Usually the park lamps and instrument cluster illumination are fuse protected, like the diagram shows, Not only check the fuses, use a test lite to check for voltage at fuse and at fusible link. The wires on top of switch in the diagram are voltage to headlamp switch, the wires on the bottom is voltage from head lamp switch to component.
Usually one of the wires from Battery positive goes to fusible links, at the moment, I don't have location.
Hope this helps, a little. I just want to add voltage and ground both are important.

there is no such thing as a fusible relay, there are relays and they are located inside the car some under the dash on driverside and some on the pass/side and then there are relays under the hood in engine compartment inside the fuse/relay box, this acar also has a fusible link or two, this is like a peice of wire but inside the wire will blow like a fuse and the only way to test is with a test light you would need to see if power runs the lengh of that link wire, these are located by the battery and then in the fuse /relay box and on the starter sometimes, the ones in the fusebox under the hood may also be metal type, heres a few picture to show you a few types of fusible links,

I am not sure about "fusible link", But the suggeation I can give you is to open dash or where the outlet is located and check the wires in the back of outlet with a light tester.

Check these;
Brake lights, backup lights. cabin lights.
None of these are controlled by the light switch which seems to be the problem. You may need a voltmeter to track this down.

A long shot is to check the fusible links under the hood. They are essentially fuses by another name. They are sometimes located in gang boxes and even one of the '+' cables coming off the battery if it has two cables.