EFI power
I went thru this issue on my Sniper. No matter where I tied into the ignition switch I would lose power momentarily either from the run to start position or the start back to run. Just the swapping of the contactor in the switch to the contacts was enough to interrupt power. This would cause the efi to reboot. I ended up with a hidden switch tied directly to the battery buss off the fuse box. I could find no where downstream of the ignition switch that didn’t cause this. My system does not use a ballast resistor and I do have the blue and brown ignition wires tied together and still had this issue. Tried a remote relay etc. My bottom line was what I believe is the spacing of terminals in the ignition switch is enough to interrupt power. This is on my 71 Demon.