Here's how the factory electrical system works:
The car has two power sources, the alternator and the battery. They're connected together with the main feeds at a welded junction. All of those wires are 'hot' when the battery is connected.
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The battery stores energy at no more than 12.8 Volts. It may read a little higher after charging, but that's just on the surface.
Electrons flow from the battery during start and when the alternator circuit can't.
Magnetism created by the electrons moving to (or from) the battery to the main junction deflects the needle in the ammeter.
When the engine is running, the alternator produces power at roughly 14 Volts. It becomes the source of power. An analogy is having a cisternor water tank feeding a pipe at 12 psi, and then turning on a water pump feeding the same pipe at 14 psi. The 14 psi water line pushes the water in the system, the tank becomes a stand by source.
More modern cars connect the battery and the alternator together in the engine bay. But the arrangement here is typical of older vehicles. When the engine is running and the battery is recharged, the ammeter shows zero. No electrons are moving in or out of the battery. If the alternator circuit fails, then the ammeter will show battery discharge when th eengine is running. If the ammeter shows increasing battery charge with rpm, the alternator's regulation is possibily faulty or the battery is very low. But bottom line it shows battery charging or discharging.
The fusible link is an undersized wire to help protect against battery shorts. Its better than nothing.
Notice the fusebox is split.
One pair of fuses is always hot.
Another pair of fuses is only hot with the key switch in run or accessory
There is one additional fuse slot that would be used for tachometer or A/C or other accessories.
The horn is not fused. The ignition is not fused. Turn signals not fused (flasher unit is sortof a circuit breaker). The headlights have circuit breaker in the switch, as does the wiper motor.
Based on what I can see in the photo, a later Chrysler electronic control unit was wired in and the schematic probably looks something like this.
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