I haven't made progress on the second O2 sensor an am thinking that I just have to find the right connector - from a '97 impreza - with a big junk yard search day when I have time.  

 

Reverse lights are go, working on 4x4 light.  I haven't found a diagram but this is what I've deduced so far.

 

RY - G and RB - GW are reverse lights.

And with the rest hooked up as pictured, I pulled a + from another source and when it is hooked up along solid line, 4x4 light is on only in low.  When it is hooked up via dotted line, 4x4 light is always on.  

I'd like it to turn on when either 4x4 option is selected, so does that mean both g and B should have power?

Since my '78 never had a vehicle speed sensor, I need to improvise something.  

Either going to buy just the reader part of this kit - $16 

https://www.smallcar.com/index.php?dispatch=checkout.cart

And buy magnets to mount on the drive shaft.  

Or maybe this kit - 

http://www.thecruisecontrolstore.com/250-4165-universal-vss-signal-generator-magnet-kit-with-pick-up-coil/

 

The signal needs to be a 0-5V Square wave, the smallcar reader is made for EJ to Vanagon swaps so I'm assuming it's good here.

The VSS in the second gen speedos reads 4 points per rotation on the speedo cable and it seems like 5ish per wheel rotation. 

So how many magnets per rotation on the driveshaft .... math ....