ahh ok
well basically if a wire isn't supplying positive, then it is grounded (it's just how it is)
so the fact that the wire is earthed when your not cranking is normal
and the zero reading you get is also normal (when you are cranking), because the trigger wire will be 12V positive, and the other end of multimeter is also connected to 12V positive (the battery), so the potential difference between the 2 points is zero volts (remember multimeter measures potential differences, not absolute voltage, essentially all measurements are potential differences anyway)
so from what you have said everything is connected up normal
if the car cranks normally and actaully starts then I cannot see any problems, voltage drop will occur cuase remember you are pulling like 30amps from the battery, somethings gota give!!
does this make sense?
