Low charge to no charge issue pulling hair out
20 amps is about right immediately after starting, but it should drop toward zero within the first minute.
I'd say.
A. If it stays at 20 amps charge, especially at slow idle, the battery charge state is low.
B. If it stays at 20 amps or more for a long period of time, connections and other weak spots in the circuit will get warm or even hot.
We don't know the total current flowing from the alternator, but for sure there is more resistance in the circuit than we'ld like.
14 - 12.4 = 1.6 drop in Voltage for 20 amps.
We can do some calculation so you can see why a resistance check using a meter doesn't reveal problems unless they are more extreme. And by then its often too late.
V = I x R
V/I = R
1.6 Volts/ 20 amps = .08 ohms
Back to finding the problems.
One problem is resistance in the circuits.
The ignition and field current on a stock 70-71 will be around 5 amps. More if a newer alternator has been installed. Same if an electric choke installed, etc.
We don't really need to know the exact current, but its useful to keep in mind if you decide to use the voltage drop to hunt for resistance points.
Follow the path the current was taking and look at all the connections along that path. Also look at places wires for those ciruits can get get exposed to chafing or heat or strain.
That's about 20 amps charging.
20 amps is about right immediately after starting, but it should drop toward zero within the first minute.
I'd say.
A. If it stays at 20 amps charge, especially at slow idle, the battery charge state is low.
B. If it stays at 20 amps or more for a long period of time, connections and other weak spots in the circuit will get warm or even hot.
We don't know the total current flowing from the alternator, but for sure there is more resistance in the circuit than we'ld like.
14 - 12.4 = 1.6 drop in Voltage for 20 amps.
We can do some calculation so you can see why a resistance check using a meter doesn't reveal problems unless they are more extreme. And by then its often too late.
V = I x R
V/I = R
1.6 Volts/ 20 amps = .08 ohms
Back to finding the problems.
One problem is resistance in the circuits.
The ignition and field current on a stock 70-71 will be around 5 amps. More if a newer alternator has been installed. Same if an electric choke installed, etc.
We don't really need to know the exact current, but its useful to keep in mind if you decide to use the voltage drop to hunt for resistance points.
Follow the path the current was taking and look at all the connections along that path. Also look at places wires for those ciruits can get get exposed to chafing or heat or strain.