Hold on. You're going about this the wrong way. First let me make a few comments. You can't "fry" the generator unless you connect the case / ground and the output terminal reversed. That will short the internal diodes, but there is always a fuse link wire in that output circuit to protect for that. Second, I'm not sure which wire you replaced, but going to a larger wire is never the answer. The engineers sized the wires to handle every possibility. If you replaced that output wire going back to the battery, you eliminated the fuse link wire, and you removed that circuit's protection. If the right two diodes were to short, you'd have a direct short to ground, a melted output wire, and likely a major car fire. You can be sure an insurance investigator will see the missing fuse link wire and any other modifications.
A fuse link wire is smaller in diameter than the circuit it protects, so it is the weak link in the chain. Its insulation is designed to not melt or burn. You can identify a fuse link wire by its dull color. The color denotes its current rating. You can buy replacement fuse link wire at any auto parts store, but you'll usually get about 12" of wire. That's enough to be cut to make three or four repairs.
Third, removing a generator and carrying it in to an auto parts store is never the right way to test them. A common 50 - 70-amp generator can take over five horsepower to run at maximum output. The bench-testers in stores have, at most, a one horsepower motor. All those can do is tell you if the generator is supplying some current, or nothing. Professional testing involves a lot more than that. All generators need three things to generate current. That is a wire, (a coil of wire), a magnet, (we use an electromagnet), and most importantly, movement between them. That's why the electromagnet has to be spun by the belt. All generators become very inefficient at low speeds. That's why all professional testers require engine speed to be increased to 2,000 rpm during the charging system tests. Bench testers can't increase speed high enough for accurate testing.
Okay, to get started, you have to understand you're changing parts in three unrelated systems, and you're inserting potentially more problems. Forget the ignition system. You don't need that if the starter system won't crank the engine. Same with the charging system. The only thing to be aware of is AMC and GM commonly used to use the larger starter terminal or the generator's output terminal as convenient tie points instead of running multiple wires back to the battery. Multiple circuits can share a terminal, but that doesn't mean they work together. What can happen is when two or three wires are connected together, it is not uncommon to overlook one and forget to connect it. This happens a lot with GM starters.
I have one more tidbit of great value. AMC used the Ford-style starter solenoid that sits up on the inner fender near the battery. There are multiple versions of those, and they all look the same. All use the two large terminals, one goes to the battery positive post, and the other goes down to the starter. That is the only wire on the starter.
There's one or two small threaded terminals on top of the solenoid. One gets 12 volts switched onto it when the ignition switch is in the "crank" position. Here's where the differences come in. That switched 12 volts feeds the electromagnetic coil inside, but there has to be a ground connection on the other end of it. In some versions, that is the second small threaded terminal. That one goes to the neutral safety switch, then to ground.
In a different version, that ground terminal is internal to the solenoid's mounting bracket. That means it won't engage if it isn't bolted solidly to the body. This is where some solenoids only have that one small terminal. When there's a second small threaded terminal it is used to bypass the ignition resistor during cranking. When the solenoid engages and switches the very high starter current onto the second large terminal, it also switches 12 volts onto that second small terminal.
The ignition coil has a ballast resistor in series with it to limit current through it to a safe value. During cranking, battery voltage is drawn down, often to less than 10 volts. After the ballast resistor, instead of finding around 9 - 10 volts at the ignition coil, during cranking you'd find closer to 4 - 6 volts. That makes for a very weak spark and hard starting. This is where the 12 volts from the starter solenoid gets switched onto the ignition coil directly. That raises the voltage to get the spark voltage back up to where it should be. In this system, that second wire does not have to be connected for the starter to work. Remember, you'll have weak spark during cranking, but we can work on that later.
I searched for a couple of hours, but I can't find a wiring diagram that reproduces well enough to be of use. The best I could come up with is this one. The red arrow is pointing to the terminal that connects to the positive battery cable. There's often a second wire attached that feeds all the other circuits including the ignition switch, so that has to be connected for the starting system to work. The blue arrow shows where the cable goes down to the starter. There will never be a second wire hooked there.
On Ford products, the plug-in "S" terminal is a red / blue wire. I've seen that drawn on the right terminal but I don't know if that was a mistake. On every one of these I've ever seen, the red / blue goes on the left, and some solenoids will have the "S" molded in to identify it as the "solenoid" terminal.
The "I" terminal on the right is for "ignition", meaning the ballast resistor bypass. That doesn't have to be connected for the starter system to work in this system. Don't forget, on some versions that is going to the neutral safety switch. In that case it must be connected for the starter to work.
If you don't accomplish anything else for now, use a test light to check for 12 volts on the red / blue wire when you turn the ignition switch to "crank". I doubt you'll need it, but here's a link to an article on using a test light:
You can do this with a digital voltmeter too, but for this type of problem, those can potentially provide incorrect or misleading results. Current has to be able to get through for the solenoid to work, and it must be able to get through for a test light to work.
I'm going to look for a better wiring diagram at home, and if necessary, we can get CJ Medevac involved. He's a "Heep" expert.
Sunday, March 24th, 2019 AT 7:43 PM