Bob P. -- Ignition Switch Woes

[patrickt]

Originally Posted by davids2toys

Wouldn't the alternator be supplying the power when the car is running either way it was connected?

Yes, the alternator is supplying the load of the MSD box whether the MSD box is connected to the top terminal or bottom terminal of the circuit breaker, but your box's load will also be supplemented by the battery as the wattage load of the MSD box changes. The current from both the battery and the alternator will be dynamic. The only real difference (other than a slight mathematical difference because there is resistance in a circuit breaker itself) is that when you have the MSD box connected to the battery side of the circuit breaker then the current from the alternator (less than 10 amps) is going through the circuit breaker. The opposite is true when you have it on the alternator side of the circuit breaker. But it's not really a big deal, so don't worry about it. And it's sure as heck not the cause of your car shutting down. The reason you usually see it on the protected (top terminal) of the CB, instead of down below on the terminal that leads to the battery, is because if for some reason that fat red wire shorted to ground you would have an electrical fire because the circuit breaker wasn't isolating the fat red wire's path to the battery.