According to ONE tech official that I know, the wiring MUST be in the car but does not need to be used. The stock wiring harness can be put in a zip-lock bag & tied to the cage (i.e. a '72 Pinto). Not sure if this is totally correct or not, but what is the difference in that & the wiring for a Mega-Squirt system? You are still modifying or deleting part of the stock harness.