I guess you are refering to the electric choke wire. The instructions do say what you state. It could be because points cars don,t usually have 12 volts there when running or they don,t want you to draw off the ignition power If you go to the fuse box you want a fuse that is only on with the switch on not one with power on always. I put one on my 64 vette years ago and due to reasons forgotten I did put it on the positive side on the coil. It runs fine and has for years. I might add that I do have a mallory electronic kit replacing the points. My 67 Chevelle was done the same way when I bought it with points and it ran fine. If you need to check it just unplug the red wire at the choke and tape it up and try it. The choke won,t work but if it still runs rough look somewhere else.