I go to the input side of the ballast resistor with a piggy back connector.
It's usually the one with the two blue wires... Just remove the wires from both sides of the ballast resistor, turn the key to run position, then take a test light with one end clamped to a ground or battery negative (-), then use the poking side to test each of the ballast resistor wires. The side that makes it light up is the input side and is 12 volts...
The other side usually has brown wires and one goes to the coil, that only has 6 volts ---> no good....
Then hook the wires back to the ballast resistor...