Three wires from the ECU feed into this connector. The yellow wire is a tach output used when an MSD ignition unit is installed, so the Atomic can control engine timing. It can otherwise be used as a 12V square-wave trigger to a tachometer. The orange wire is an A/C kick-up wire, which compensates for the added load on the engine from an A/C compressor. Neither of these wires were connected at this time. The white wire is the tach input wire for the EFI, supplying the rpm signal from the distributor or ignition box.