Chasing wires

[Jens Wendorff]

Doing this and that over the weekend, I thought I can finally connect my heater blower in the engine compartment correctly...
I cleaned the contacts on the switch at the handbrake assembly and confirmed that it works.
From there, 2 yellow wires are starting.
Both are going through the center tunnel inside the big cable bundle running into the engine bay where the starter is.
I found (measured)that 1 has connection to ground (where?),
the other one has a connection to the lower left pin of the 14-pin connector at the rear fuse panel.
From there, it starts together with a second one (yellow or yellow/black) and is vanishing in the engine harness.
This second one is obviously connected to the plug located at the left side chain housing.

Now the ??? start:

How is the blower to be wired correctly, and where can I assume to find the plug/loose end?
Is the wiring measured so far correct?
And what is the purpose of the plug at the chain housing?

I am pretty bad in electrics, so every help is appreciated!

Jens
'76 2.7 CIS with '73 body conversion