Remind me again where this wire goes?

On my 78' there is a small bundle of three wires that run from the left side of the engine to the right, underneath the coolant manifold in the valley between the carbs. One wire goes to a sender (don't know what it is) on the bottom of the coolant manifold. The long one goes all the way across to the A/C compressor. What does the other wire go to? For the life of me, I can't remember where this wire goes and there's not an obvious sender near the wire. Help!

 

It's a little tough to tell, but it looks like:

wire to underside of coolant manifold - white/black (maybe gray/black)
mystery wire - red
wire to a/c compressor - black

 

You're right, it is just grey. Dirt on the wire made it look like a black stripe.

Ok, this explains a lot. My car does not have this valve and I don't think the wire was connected to anything. When I was test running the engine, I saw a wisp of smoke coming from this area. The connector was grounding against the intake and the heat from the short melted part of the insulation and was smoking. I'll make sure I secure this wire before continuing.

Thanks Steve!