Most older coil setups have 2 "+" wires.
These types of Coils heat up too fast and fail if you send then 12volts all the time.
So the setup was 12volts when starting only, then 8volts while running.
The wiring was a regular wire from the starter solenoid, it would be connect to the "+" on the coil and the Starter motor wire post on the solenoid(or the "I" post if it is a 4 post solenoid), so coil only has 12v when starter is turning over the engine, it might also have a diode.
The second wire is a "resistor wire", or there would be a ballast resistor.
It comes from the key switch(or ignition module) as 12volts, then passes through the resistor which lowers it to 7-8volts which is also connected to the coil "+".
This is the voltage to the coil when driving, so no over heated coil.
You can re-wire it yourself, you can buy ballast resistors at any auto parts stores, that's the part you really need.
The wire to the solenoid can be left off but does help on cold starts.