PCM 5V Speedo Signal?

[Ace]

I was about to perform a PCMectomy last nite after I decided the truck no longer had any use for it. The WIF sensor went MIA when I went to the big fuel filter awhile back. I recently decided the grid heaters would be staying on the shelf and pulled the relays out too. I was under the impression that was all the brain box was doing for me before. But evidently it provides 5V to the speedometer. I unplugged it and that was the only thing that didn't work anymore.

I checked the wiring digram and it says there is a "speed sensor pickup" on pin 47. That's the only thing on there that looked to me like it might be what I was looking for. Anyways, that pin has 5V on it with key switched on. Can anybody confirm whether or not I'm barking up the wrong tree here? And maybe suggest a workaround?

[Ace]

Y'all gotta help me figure this out. These things are getting expensive and hard to find. Someday they may not be available at any price. I just spent all afternoon playing with this thing and cannot make the speedometer work without the PCM! Here's the pinout diagram:

I got a 5v regulator and applied 5v to the one called 5v supply (6) and several other just shooting in the dark. The three indicated as ground are ground as they sit on the plug, unplugged. What is SCI?

The only thing I can deduce is one of these is an input from the signal generator and another is the output back to the speedometer, Is it routed straight through, amplified, or what?

There's got to be a way to make the speedo work without this big honkin' black box!