Fried ECM
Run side is almost always Blue.
Coil/Start side of ballast should be lower when current is flowing, so that's OK.
Schematic is like this. Feed wire to ignition switch may be red insulated in your car and year.
Here's your test.
When the current flows through the resistor, it loses Voltage. So that's OK.
But when the current flows through the circuit, it should not be losing any voltage.
In reality, there is resistance. Depending on the current draw, a half volt might be acceptable.
1.7 Volts with only 4 or 5 amps draw indicates a problem.
When the engine is running, current should be flowing from the alternator.
If there is bad connection on that wire, that would heat up and get worse as it runs.
You can do a visual check on the connectors and terminals.
A search here for Packard 58 and Bulkhead connectors will turn up photos for you.
Should be 0.5 to .7 Ohms at air temperature.
12.0 to 10.6 V is a big drop between the battery and the ignition wire. Check every terminal and connection.
Run side is almost always Blue.
Coil/Start side of ballast should be lower when current is flowing, so that's OK.
Schematic is like this. Feed wire to ignition switch may be red insulated in your car and year.
Here's your test.
When the current flows through the resistor, it loses Voltage. So that's OK.
But when the current flows through the circuit, it should not be losing any voltage.
In reality, there is resistance. Depending on the current draw, a half volt might be acceptable.
1.7 Volts with only 4 or 5 amps draw indicates a problem.
When the engine is running, current should be flowing from the alternator.
If there is bad connection on that wire, that would heat up and get worse as it runs.
You can do a visual check on the connectors and terminals.
A search here for Packard 58 and Bulkhead connectors will turn up photos for you.