70 GTX New modified wire harness -New plug what is it for?

[Azmotorhead]

70 GTX 440 4spd. I purchased a new engine wiring harness thru Year one(M&H Harness). It was built with the electronic ignition modification. Which incorporates a 4 pole ballast resistor and 4 pin socket for the ECU. Added into the harness is a new plug up by the firewall junction. It is one female terminal with two wires Grey/black stripe and Black/yellow stripe.
It's Sunday so I cant call M&H, but thought the brain trust here may know what the plug is for. I rang the plug out and it has continuity to the ballast resistor leads and the coil terminal. My thought is that its for the tach plug.
Existing harness has a separate one wire Grey/blk stripe that passes thru the firewall by itself I imagine that is the original tach lead.
pic of connector

 

[BeepBeepRR]

Tach wire. On the other one I see in the 70 Charger schematics a black with a yellow tracer for hood mounted turn signals. But it doesn't show a grey with a black tracer. So I am unsure of the use. I did not see these same wires on the 70 Belle/Sat/GTX schematics.

 

[Azmotorhead]

M&H answered my question.
Their connector connects to the tach lead that passes thru the firewall(grey plug in my picture).
Grey blk stripe wire is the tach signal. Black yellow stripe is signal wire to ECU.