Hey there
@pwfree! I'm still here and working on my K project as I have time.
I actually ditched the BEP 3.0 early in my build since I didn't find it necessary. I found that the only reason I kept it on board was for the alternator exciter circuit which I wired a resistor in line and connected the exciter line to a +12v source on the M-Unit Blue. I have completely rewired the bike removed the bulk of the OEM electronics including the Motronic since the wiring of this post.
But to directly answer your question, you hook the fuel sensor signal (post the modification for digital gauges) to the Breakoutbox B's "FUEL" input. Check your model year's Clymer's for the following wiring colors. I'm not sure if '85 K100s came with a fuel switch or a variable sender. As I'm not as familiar with the wiring of the fuel sender (or switch) on a '85 K100. The below is based on my '93 K1100.
FUEL SENDER CONNECTOR FROM THE TANK:
Fuel Level Signal ––– Yellow ---> Connect this to "FUEL" on the Breakoutbox B.
Low Fuel Indicator ––– White ---> You could leave this wire floating or wire it to an external light. I have it floating.
+12v Power ––– Black
Ground ––– Brown
Keep in mind that you will need to calibrate the empty reading and the full reading manually in the Motoscope Pro settings per the manual.
Oil pressure input: The oil pressure switch which is located at the water pump and runs up through the channel from the HES sensor. This should be a single wire, connect this to the "OIL PRES." input at the BreakoutBox.
Water Temp Sensor: I used the temp sensor at the water pump and ran the wire to "H20 TEMP." on the Breakoutbox B This is how it's set up OEM on the K lunchbox. The second H20 sensor at the top of the engine just under the radiator runs to the Motronic (I have this running to the Microsquirt).
Then for the Motoscope Pro to get all these signals is the orange wire from the Motoscope to the "BUS" input at the Breakoutbox B.
H20 TEMP SIDE NOTE: I think that there might be a need to add a resistor(s) inline before the connection to the Motoscope Pro to adjust the temp reading accurately. But I haven't quite landed on if this is actually needed. Reason being, The temp sensor at the water pump gives a different reading than the water temp sensor that goes to the ECU (but accurate) from what I can tell viewing what the Microsquirt is reading.
I don't know how far you are wanting to go in the wiring of your K, but I found that the BEP 3.0 was just taking up room for only for using the alternator charging circuit functionality. Since you are going with the Motoscope Pro, your gear indication is actually programmed once you are riding except for the neutral light. I've left my gear indicator/neutral switch wiring from the transmission floating until I build a logic circuit to detect ground when only in neutral. This isn't a priority for my project at the moment.
I hope this helps! As robmack mentioned, you'll need to test to sure your sensors are compatible. I was lucky and everything seemed to work as expected.
Sorry if this was more info than you were expecting.