You're over-thinking the fuse link wires. They are simply a short piece of wire that's of a smaller diameter than the wire it protects, making it the weak link in the chain. Also, their insulation will not melt or burn. I pointed out one of your fuse links with the blue arrow. This circuit has nothing to do with the starter circuit. GM simply likes to use the large copper terminal on the starter solenoid as a convenient tie point rather than running that wire all the way back to the battery. Often, you'll find two or three fuse links attached to that stud.
You can buy replacement fuse link wire from an auto parts store. They come in lengths roughly 12" long and can be cut to make multiple repairs. The color of the insulation denotes the current rating, just as it does with regular fuses.
The length of fuse link wire you splice in is not important. It only takes a fraction of an inch to protect the rest of the wire.
Fuse links are not intermittent. As with regular fuses, when the wire burns open, it's done and has to be cut out and replaced. While I've never seen this, it might be possible to develop a corroded solder joint where the link is spliced to the regular wire, but as you can see on your car, those joints are sealed with moisture-proof heat shrink tubing. That has a hot-melt glue inside to seal better than regular heat-shrink tubing.
Unlike regular fuses, there is one thing that really causes some confusion with fuse link wires. When the wire burns open, at the end of the process there's some arcing that leaves a carbon track behind. If there's no load on the circuit, meaning no current trying to flow through that carbon, a digital voltmeter will "see" the full 12 volts further down the line. That falsely tells you there's 12 volts there and the circuit should be working, but it isn't. Here's where I tell people to use a test light instead of the digital voltmeter. Test lights operate by the current flow making the bulb light up. This has to be a standard, inexpensive test light, not one of the new ones with all kinds of circuitry inside. The test light will correctly show the circuit is dead. You can prove this to yourself even further by testing with the voltmeter first and finding the false 12 volts; then test with the test light at the same time while the voltmeter is still connected. You'll see the 12 volts drop to 0 volts as soon as the test light is connected.
Fuse link wires are used in some circuits because of their "slow-blow", or delayed response characteristic. This makes them desirable for motor circuits because those have a very high starting current that drops to a safe level once the motor gets up to speed. If a regular fuse was used for a radiator fan motor, for example, the fuse would have to be big enough to handle that high start-up current, and that could make it too big to protect the wiring if the motor developed tight bearings. Fuse link wires won't be used to protect a computer because if something inside the computer were to short, the wires and other parts of the computer would be damaged by the excessive current long before the fuse wire finally burned open. The only time you might find a fuse link wire feeding a computer is when that circuit also feeds other things that do draw high current at times. In cases like that you might find as many as a dozen wires branching off from one fuse link wire.
To test a fuse link wire, just gently tug on it. If it feels like a wire, it's okay. If it's burned open, it will stretch like a rubber band.
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Sunday, October 24th, 2021 AT 6:06 PM
