Quote: Originally Posted by eCar?
I still don't know what you needed the diodes for.
If you not using diode, there maybe some stupid things going to happen to your car. Car makers design to cut off the ACC line while cranking is to minimize electrical usage (radio and other stuffs) so that the starter can get all the juice from the battery to start the car. If the ACC line is not cut off, the battery voltage can drop very low and the car will have a hard time to start.
Using diode on the ACC line keep all circuit on the car's ACC line off during cranking.
Using diode on the IGN line keep all circuit such as fuel pump, ECU, AC and other off while the key is in ACC position.
The combine wires with diodes keep the car's electrical system remain AS IS.