When working with the Ammeter wires......Make sure the battery is disconnected first. Both wires are Hot, and the black wire is NOT a ground.
An important point!
Black wires are often power wires.
Lets begin with this. All of the wires connected to the battery are hot when the battery is connected.
The only protection from a dead short (battery to ground) is the special 16 ga wire called fusible link.
Wires on the factory diagram all have codes.
A is Battery. 1 is branch, A is segment. 10 is wire gage, R is red
R6 is Alternator output
J1 is feed to ignition switch
Now lets go to how the system is laid out to get power to where we want.
I find it helpful to recognize the car has two power sources; battery and alternator.
The battery provides power at 12.8 Volt at most.
The alternator provides power at around 14 Volts. Just like water or air pressure, given the oportunity, electrons will flow from the high voltage source to the a voltage. We call the movement of electrons current.
On the car, the battery and alternator each has an output line that is tied together with the main circuits at a welded splice.
Unlike recent generation of cars, this splice connecting the battery and alternator to the main circuits is in the interior harness.
On the diagram below it represented by a solid circle. But the '71 Service manual shows splices as diamonds.
Everything connected to that splice is connected to the battery positive.
It doesn't matter if the key is off. They are still hot. This why the horn, the brake lights, the dome light, etc will work with the key off.
Ammeter: The ammeter is in the battery feed. The needle deflects when electric current flows past the needle. So it will show disharge during starting and charging after starting. Normally its in the middle since the alternator supplies power when the engine is running. If your 71 has had a leak over that area of the dash and Redfish has explained he had seen to be a cause of occassional problems including ammeter connections. Redfish also posted not seeing ammeter issues with ralley dashes. He saw more dashes than most working in the dealerships etc. Point is its a useful tool, not a boogeyman, and the only time power flows through it is for recharging and starting or turning somehting on when the alternator is not running (ie dome light).
Main feeds: From the main splice there are three or four main feeds.
J1 Power to key switch. This is vulnerable to resistance and therefore heating at the column connector.
H1 power to Horn relay. This is only 16 gage wire since it only has to power the horns
L1 power to headlights. This is only 16 ga wire since it only has to power the headlights. (unfortunately the rest of the headlight wires are 18 ga)
Q2? (Might be Q3) Power to fuses that are always hot. 14 gage wire.
The battery feed when connected should allow the dome light, brake lights, horn, etc to work. If they don't work, then check that circuit.
