1979 Chevrolet El Camino reversed battery cables

GM commonly used the larger battery terminal on the starter solenoid as a convenient tie point for other circuits to tap off of, and that's where you'll find one to three fuse links. Tug on those wires. If they're okay, they'll act like a wire. If they're burned open, they'll act like a rubber band.

The advantage to using fuse link wires is they take a while to burn open. It takes considerably more than a momentary short or reversing the battery polarity. The biggest thing you have to look at on a '79 model is the generator. They have six diodes which are one-way valves for electrical current. When the battery is connected correctly, those diodes are in the circuit backward. That's what prevents the battery from discharging through the generator when the engine is off. With the battery polarity reversed, those diodes are "forward biased" meaning they're turned on and act like a dead short. While a fuse link protecting that circuit also would take some time to burn open, some of the diodes can short instantly from the excessive current of a reversed battery. Once they're shorted, they're shorted permanently and will act like a piece of wire. THAT'S what will burn that fuse link open when the battery is connected correctly. It's not practical to replace the diodes. While it can be done fairly easily on that older style generator, the parts will cost just as much as a rebuilt generator with a warranty.

To test for this, measure the voltage on the large output stud on the back of the generator. If you find full battery voltage there, the fuse link and generator are okay. If you find 0 volts, replace the generator, then look for the fuse link in that fat wire that goes back to the battery positive terminal. I would expect to find additional wires bolted to that stud in that case too, and that would explain why some circuits are dead.

You're only the third person to note the "alternator" story. In an effort to use correct terminology with my students, it must be noted that Chrysler developed the "AC generator" for use in 1960 models and copyrighted the term "alternator". GM and Ford followed with their versions three to four years later. While everyone will know what you mean when you ask for an alternator, the industry-standard term now is "AC generator", or just "generator". That's the term you'll find in service manuals too.

The Chrysler charging systems switched from a mechanical voltage regulator to an electronic one in 1970. Both the older and newer systems were real easy to diagnose and repair and were the best system there was. In my opinion, GM's version with the built-in regulator, like you have, was the world's second best design. They didn't cause a lot of problems, and those that did develop were pretty easy to diagnose and fix. One thing you have to watch out for though is to mark the two case halves so you can put it back together the same way. They can be reassembled four ways, and three were used depending on the application. If you can't find the right application in stock, you can use a similar one by removing the four case bolts and swiveling the rear half as needed. Just don't pull the case away because that will allow the brushes to pop out of their holder. Reinstalling them isn't hard but if you've never done it, you'll want to ask how to do it first instead of breaking them.

Your design was used through 1986. For '87, GM came out with redesigned starters and generators and they really screwed up the generators. Those are the world's biggest pile and they haven't done anything to make them better.

A fuse link, or fuse link wire, looks like any other wire but it will be a short piece of a different color that's spliced in. Typically they're less than six inches long, and they'll have a dull finish, not the normal shiny insulation most wires have. The wire is exactly the same as any other wire, but it will be a smaller diameter than the wire it protects, making it the weak link in the chain, so to speak. The major difference is the insulation will not melt or burn.

You can buy replacement fuse link wire at any auto parts store. They go by color which denotes its current rating, just like with regular fuses. Typically you'll get a piece about 12" long which is enough for two or three repairs. You can also repair the old link by cutting away the insulation until you find the ends of the wires, then you can splice and solder them together and seal it with heat-shrink tubing. As long as some of the original wire remains, the circuit will still be protected.

One other point that is worth mentioning is fuse link wires have been responsible for confusing a lot of people experienced in electrical diagnosis. When the wire burns away, the arcing leaves a carbon track behind inside the insulation just like what can develop inside a distributor cap. That carbon track can't conduct enough current to do anything, including run a test light, but if everything down the line is disconnected, the little tickle of current that can get though will be picked up by a digital voltmeter and incorrectly show that voltage is there and the link must be okay. This is a perfect example of where the cheap test light is more accurate than any voltmeter. This would be similar to where a closed valve in a compressed air line won't let enough air through to run an air tool, but if there's just a tiny pinhole leak, eventually enough air will sneak through to register on a pressure gauge. No air goes THROUGH a gauge, just like almost no current goes THROUGH a voltmeter.

Most of the fuse links GM used by the starter solenoid were gray or black. Other common colors are dark green, orange, and white. I don't recall ever seeing a red or blue fuse link. If you want to see exactly what they look like, look on any front-wheel-drive Chrysler car from the late '80s to early '90s in a salvage yard. There will be a whole pile of them tie-strapped together, going around the left strut tower. They come out of a black plastic triangular block where they're spliced to the fat feed wire, usually red.