^^^^THIS^^^^
Read Redfish's post carefully, and take notes.
Let me explain why I so strongly suggest following Redfish's advice and why I so marked disagree on the earlier posts.
Redfish's explanation correctly describes the power flow, and why the RTE unit, if needed, is safer.
Now lets get to power flow.
When the engine is running all of the power should be coming from the alternator.
Power from the alternator
does not go through the ammeter.
The only current flowing through the ammeter is current to recharge the battery. If there is a winch or plow wired to the battery, that would be an exception.
In spite of the fact that the ammeter is labeled 'Alternator' it only indirectly indicates alternator output.
What it really shows is current flowing to or from the battery. IF the battery is discharging during normal driving, you can assume the alternator is not working.
Why is this?
Because electricity always flows from the highest voltage power source.
The battery's power is available at 12.8 Volts give or take some.
The alternator's power is available at 14 Volts give or take some.
Here's a diagram showing normal current flow with orange arrows.
View attachment 1715598761
That little bit of current flowing down the accessory circuit is going to the IVR.
Specifically it goes through a welded splice to terminal at K on the connector. There is no fuse for this subcircuit.
View attachment 1715598762
This changed at some later model but in a 67 rally harness, K is blue with white. F is black. The blue with white was eventually deleted. The one black switched 12V feeds brake warning lamp, oil warning lamp, and the limiter.
If your Barracuda had been optioned with a tach, it was supplied 12 Volts from a fuse connected to the accessory buss in the fuse box.
I just recreated that for my car so I can show some photos in the next post.
