[Lynn Eades]

Some of the wire used to rewire your carrier is too light for a six volt system. (blue at resistor goes to a skinny white) It's might be fine for a twelve volt system.
The cross sectional area of the wire looks too small.
If you apply six volts to that resistor , you should get 4.2 out the other end.
If you have a high resistance (voltage drop) before the resistor ( in a switch, or corroded terminal etc)under load it will drop your input voltage.
Hook your resistor up direct from a battery, through a test light or bulb, and then apply your volt meter, to check your output voltage. Then you know its not your resistor.
Note. The voltage in your primary ignition circuit varies depending on points being open(0 volts) or closedResistance of coil), changes when cranking, and again when running.