I'm no expert but fusible links are usually rated by size not amperage. Don't know about the 69 but I believe the 68 has a black 14 gauge fusible link connecting the horn relay to the main car power up wire. Usually the fusible link is 2-4 sizes thinner than the wire it is protecting. Although I do have an orange link that is labeled 40 amps. I thought the headlight switch was powered from the ignition switch, which is inside the cabin. There should be no fusible links inside the cabin of the car. I think your headlight switch has an internal thermal breaker, don't know what the amperage of that is. If your headlights are going off and on it could be the breaker in the switch tripping and setting. If you are going to install the relays for the high and low beams 16-18 gauge fusible links will work. Doesn't take much power to turn those on.
When I opened up the main splice just rear of the alt it didn't look too good. Not sure what or when but that baby must've got pretty hot at some point. Those wires were in pretty bad shape. Melted all the way thru the wrap and was probably making contact on the intake. I'm glad I caught all this before the fire. Anyways it's all getting replaced so I needed to replace the fusible link as well. Not being too elect savvy I wasn't sure what that was going to take. Boned up a bit and found that they are hanging on the parts store shelf. The wire that feeds the headlight switch is 12ga so I went with a 16ga link. We'll see how that works out. The original said 14-16. Got almost everything done yesterday. Just have to jack up the car and replace the 8ga to the starter and wrap everything back up. Took awhile to sort out all the wires( those wires for the wiper motor are a mess) but I got the new alt mounted and everything run where it's got to go. I'm getting good at soldering and heat shrink tho.
Looks like you did a good job with the terminal ends, crimp, solder and heat shrink is way better than using the insulated crimp-on terminals.
The main splice heating up is a common problem with these old cars, especially when extra amp draw is added with accessories, all the power for charging the battery and powering up the car goes through that splice. New and stock they worked well but over time with increased resistance and draw they can generate heat which causes more resistance and more heat etc... Upgrading to a terminal block or modifying the horn relay as a terminal block is a good way to eliminate heat at the splice.
Sometimes the fusible links can get confusing if they are thought of as fuses or breakers. With a fused circuit the amp draw is calculated and a fuse is selected for a draw over that rating to protect the component or circuit. With a fusible link the link offers a lower rating than the wiring in the circuit and fail before the circuit wiring. The fusible links are wrapped or encased in fire resistant insulation, that keeps the car from burning up in an electrical fire. They are usually installed in main unfused circuits and there to protect the circuit, that's why they are usually chosen by wire size rather than amp rating. Sometimes a fusible link greater than four sizes smaller is chosen, if the component draw is not high. An in tank fuel pump may need a number 10 wire size, not due to a high amperage draw but to reduce voltage drop in a long run. The longer the wire the more voltage drop if the wire size remains constant. Using a larger gauge wire will reduce voltage drop but can be protected with a #18 fusible link. The smaller the fusible link the faster the circuit protection in case of a dead short to ground.
My friend up in Cobble Hill recently had a fire in the trunk area of his 67 Bird, The heavy gauge wire to his in tank fuel pump shorted and started to burn, fortunately they extinguished the fire before it burned the car, garage and attached house to the ground. The battery is in the trunk but the pump wire went from the battery to the dash and back to the pump. A number 8 wire was used with no fusible link. Would have been better to put a relay in the trunk to power the pump and use a small gauge wire to control the relay from the dash. That car is mechanically great, from the roll cage to the diff, but electrically it needs major surgery.
