Holley sniper install

"Shielded wires" are not that simple. You have to understand that the factories have spent millions of dollars on R&D. --And understand that each "build" is just a little bit different from the next. You have to do some research on proper grounding, etc. It ain't easy, and there are too many variables. And there are several issues with grounding/ shielding/ RFI/ EMI. One BIG issue is "ground loops." This is where improper grounding, sometimes caused by multiple grounds, have a current flowing in the ground system, and cause a difference of voltage. With modern electronics and sensors, this does not have to be much

Another angle is electromagnetic (EMI) which we used to know in plug wiring as "crossfire." This is where a wire with enough power--like the alternator charging wire, or sometimes plug/ seconary wiring, generates enough magnetic field to induce current into a nearby wire

This is brought home by warnings over at MSD. Let's say you have an MSD ignition you have added---and I'm not even referring to EFI yet----in some situations, THE MSD HAS FALSE TRIGGERED ITSELF!!!! This is because the high power in the MSD plug wires can induce a false trigger into it's own trigger wiring.

proper grounding strategy for holley efi - Google Search