But, for the ammeter to function properly, does all power need to be routed DIRECTLY to the ammeter, and then branch from there?
The ammeter is supposed to indicate power going to/from the battery so you can tell if you are charging or discharging it. For that to work, you have to have the battery on one side and everything else on the other side of it.
In some vehicles, the starter is an exception to that. It is the highest draw item in the vehicle and can be bypassing the ammeter. You would have to check the factory wiring diagram to see how your should be wired.
The 80s S10 had a very nice solid copper bus bar mounted to the passenger side of the firewall. I have used them on a few projects. If you have a junkyard nearby, you might check it out.
