Curiouser and curiouser!

I'm beginning to get a bit confused. Everything seems to be according to Hoyle per the diagram, but for reasons yet to be determined, there is no voltage getting to the coil on the relay. I'm beginning to suspect a bad wire, since that is really th only thing that it could be. I wouldn't mind somebody looking over my virtual shoulder here and seeing if I missed a trick.

Here's what I've done so far:

• Fuses OK, and clean contacts - voltage check shows connectivity
• Checked the two underhood switches (Pressure switch OK, Thermal switch bad - have shorted the leads for that switch so that is worked around for now)
• Checked relay - works fine out of the car - contacts sparkling clean, too.
• There is voltage present at the leads for the thermal switch (which also confirms the pushbutton switches by inferrence), so there should be voltage going to the relay coil at that point (when the leads are connected and car is running)- but there isn't! According to the diagram, there is nothing but a wire between the ETR Switch and the relay coil, but the wires at the ETR switch don't match the color code on the diagram for some reason, and they appear to go back into the car under the dash and come out a different color (Black/Red/Green) to the connection on the relay. They all look original, and un-messed with. They are going to something that isn't working!
• I have tried circumventing the relay by connecting across the sockets manually, with the relay out, and the clutch engages and the AC runs fine then, so it's just a matter of getting voltage to the coil.
• I have checked for bad grounds. - found none

So... it appears that the problem is somewhere just after the ETR switch (in a wire?), but the diagram isn't telling me the whole story. I have even pulled up the fuse box to look underneath and all the continuity is intact from the Black/Red/Green +V wire to the socket for pin 86 of the relay. The wires from the ETR are Blu/Br and Br. Where does it make the change to the Black/Red/Green wire??

I've looked under the dash for the Black/Red/Green wire and have not been able to locate it, but that's where it goes from the fusebox. I tested, and the B/R/G wire is not shorted to ground.

Suggestions? A German wiring de-obfuscation macro I can use or something? All the diagram shows is a Black/Red/Green wire between the ETR switch and the relay coil.
Most vexing, I'm soooo close, but I'm running out of ideas! Will I really have to pull out the pushbutton cluster? It seems to be doing what it's supposed to, or I wouldn't get voltage at the ETR switch, would I? I guess I can go check the current flow, but that's pretty silly.