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Hello Jim,

I used to owe a 464 that I refurbished completely, it had a DM44. I don't possess it anymore as I gave it as a gift to a friend...
I disassembled the Vertical Pre-Amp board and the Triggering board quite a few times and remember quite well of this wire.
I'm not sure at what revision of manual and or schematic you're looking, but on the 464 manual that I have, it's really easy to spot this connection at both its ends.
On diagram 3, VERTICAL SWITCHING, it's on the right side, a little bit above half of the page. from top to bottom, it's the first outgoing connection just after the outputs to the delay line, coming out from one of the ganged switches actuated by the TRIG-VIEW button. It gets connected to +15V when TRIG-VIEW is pressed, and it goes to R691 on diagram 5.
On diagram 5, A&B TRIGGER GENERATOR, this connection show on the very bottom of the page, just above the "A&B TRIGGER GENERATOR <5>" diagram title.
When the TRIG-VIEW button is pressed, the +15V coming through this wire is what actually provides power to the TRIG-VIEW output buffer, which will source the TRIG-VIEW signal.
It's not clear to me though, why Tek chose to switch the power going to this small output stage, since its output is further switched by the remaining contacts of the TRIG-VIEW switch.

On the 466, I have only a PDF copy of a later revision (whose channel select circuitry is similar to the 465B and 468) and there doesn't seem to exist this wire, as the whole TRIG-VIEW circuitry is completely different.

On the 465, at the source of the signal (red wire) it's represented exactly the same as I described above for the 464, and in the same location of the VERTICAL SWITCHING <3> diagram, with the only difference that the wire is not connected directly to the board, but by means of a connector pin, P337.
Yet on the 465, at the other end of this wire, it's different from the 464 schematics, because Tek chose to draw the Trig-View amplifier on a different diagram <11>, and there are a few differences in what the +15V coming through this wire actually does. On the 465, it only apply bias to the Trig-View amplifier input transistors (while the output transistors get continuous +15V supply).

Regarding the scope being with DM44 or without it, I don't think it matters whatsoever to this circuit.

Last but not least, regarding the two different versions of the custom Triggering Amplifier IC, 155-0032 or 155-0217, I don't think it matters if with or without DM44t... There's nothing about this IC that holds any relation to the DM44 being installed or not.
When I got my 464, its trigger was not working well, and it had 2 different versions of this IC (A time base had the older, B time base had the newer).
It was one of my first questions to this group, back on 2016, whether there was any difference between them (that could justify my A trigger was not working well) but soon enough I discovered that my problem was due to a leaky FET (at the A trigger input stage). The leaky FET was causing a DC offset at the input of the Trigger IC, beyond of what it can handle.
After I located and repaired the guilty FET, I was able to even swap the ICs between A and B, and they proven to be interchangeable to the point of barely affecting the trigger calibration / adjustments...
From the answers I got from the group back then, IIRC, the only difference between them is that the later one is made on a newer silicon process. They're equivalent and interchangeable.

KRgrds,

Fabio