Hi all, first post here!
I’m having an issue with my charging system. Just replaced the alternator and the battery. The charge light now comes on at higher rpms which indicates high resistance to me, though when it comes to electrical diagnosis I’m way out of my depth. When I start the truck and disconnect the battery cables the engine dies. It’s definitely not charging.
I have yet to verify that the external voltage regulator is working, but if it’s not I’d like to transition to a gm or ford alternator with integrated voltage regulator and I’m wondering if anyone has experience with that swap and could advise me.
The wiring on this truck is hacked up garbage so I’m seriously looking into investing in an overhaul. Do y’all have any recommendations for custom built harnesses? Or alternate solutions? I’m so out of my depth with electrical work and I’d love to troubleshoot it all myself but I work as a shipwright full time and spend enough of my days troubleshooting dumbassery.
I’ve been learning a lot on this forum, thank you! Keep rollin

 

That's a perfectly normal occurrence. The battery provides the field coils with their power, enabling the alternator to charge the system. Without the connection to the battery, the alternator doesn't do anything more than sit-n-spin. Since the battery is disconnected, too, the entire electrical system isn't getting any power from anywhere, so the engine shuts off. The battery is an essential part of the vehicle's entire electrical system. The engine won't run without the battery in-circuit. Essentially, the vehicle runs off the battery, and the alternator maintains the battery charge at a predetermined voltage.
If you have a multimeter, a very inexpensive investment, but a massively useful piece of test equipment, you can check the voltage to see if the battery AND the alternator are working properly. The battery should read around +12.6 VDC across the terminals when the engine is shut off. That tells you the battery is good, and properly charged. Once the engine is started, there should be about 14.5 VDC across the battery terminals. That tells you the alternator is functioning correctly, or not.
Did you check the battery terminals for cleanliness, and corrosion buildup on them? Especially where the wires connect to them. It's easy for battery acid to get into the wiring, and corrode the wires inside the insulation. Hard to see, without using a multimeter to ohm out the wires. That would tell the tale.

A special note: Before ohming out ANYthing in the electrical system, always remove BOTH battery terminals. It only take a very small amount of voltage running through the meter in ohms mode will destroy the meter's ohm circuitry. From the looks of things, remove the terminals from both batteries.
Or, is the box on the right the fuse block? If so, don't bother with it.

Also, check the resistance from the body, engine block, and head, to the battery negative terminal. The resistance should be very low. Like below 1 ohm. Preferably below 0.5 ohms. A bad ground, which is what those are, can cause all kinds of fits. There should be a ground wire going from the alternator, or the voltage regulator, or both, to ground. Usually on the head near the alternator.

Check the heavy duty wire going from the voltage regulator, or alternator, I'm not super familiar with the system, to the battery positive. Make sure that both ends are clean, bare, shiny metal.

Electricity isn't as mysterious or magical as people think it is. By the same token, I made my living working with electronics/electrics my whole life, so...
Just make sure to respect it. Don't fear it, but respect it. Like, don't cross the battery terminals with a metal object, just for example. You can get a real nice spark shower that way, weld the object to the terminals, and ruin all kind of wires, the battery, etc. Don't be afraid to use the multimeter to check the voltage, but don't drop a wrench across the battery, you see?

Good luck, and let us know how things work out for you!
​​​​​​​Pat☺