69 C10 with 2011 LS3

[RManson]

Most aftermarket ECUs require a straight battery connection. I know this isn't an aftermarket deal but I assume it's just as sensitive to voltage drop, etc. I would run the 12V constant and ground wires from the ECU directly to the battery and the 12V switched wire to the key switch. When the 12V switched wire is triggered via the key switch, the ECU will power on and vice versa. This should also overcome your "not switched at cranking" problem as well. Put a big fuse inline between the battery and the ECU if you're worried about it, but if you dig around in your harness, there is probably either a circuit breaker, fuse, or relay already installed that protects the computer. Good luck!