So looking at an online wire diagram (correct part number?). Looks like the red is a power lead and the gray is a tach feed. However there is a red ignition feed.
So my guess would be that the two wires bundled together would be ignition and tach.
(The reason I said tach filter is the pulses may not work for the older model tachs. Try it without the filter first then).
If your going points here is the diagram, not sure of your part number though:
