Distributor to ECM Question

I have another wiring question as I plan my marine TBI conversion. On my current carb configuration the four terminal connector that connects to the distributor is used only to lock the distributor when setting the timing. I noticed in the attached diagram for my ECM there are four wires coming off the distributor and going to the ECM. White to D4, Purple/White to B5, Tan/Black to D5 and Black/Red to B3. I understand the connection, however how does the timing get locked down to set the timing, or is that function now performed by the ECM? Anybody know a good part number for that four pin connector that attached to the GM HEI distributor. Thanks again.

Attachment 16839

That 4 pin connector is the same as an IAC although the wire colors aren't the same. Most aftermarket pigtails will have all 4 the same color anyway :rolleye: You should be able to disconnect the bypass wire to put it into set timing mode.