K100 Fuel pump circuit failure outside of tank

[ironandsteel]

1987 K100RS - getting running after sitting for years.

I am trying to debug the fuel pump circuit. I have verified the wiring from the 4 pin connector to the pump. I can apply 12v to green and ground brown and the pump runs. So- the issue is not inside the tank.

I do not get power to the green/white wire at the motorcycle side of the 4 pin.  The fuel pump relay clicks when ignition is on. It connects pin 87 to pin 30 to turn on the pump. If I pull the relay, I do get 12v on pin 30. I can jumper 87 to 30 and I still do not get 12v on the green/white wire at the tank connector.

I know that fuse 6 is for the fuel pump, and it is good. I don't understand where the fuse happens in the fuel pump circuit, though. I do not get continuity from pin 87 of the relay to fuse 6.

I have disconnected, cleaned, reconnected all the various connectors under the tank. I removed and cleaned the brown ground wires that bolt to the frame.

I have not found a decent, legible wiring diagram that shows the wire colors and the relay numbers. This would clear up a lot. Any pointers to a good hi-res wiring diagram would help.
Thanks!

[Laitch]

It might be helpful for you to download BMW's LE Jetronic training manual from our site to understand how the electronics work.

First off, at the fuel injection relay there are two 87 outputs—one line from 87 and another from 87a on a five pin relay or two lines from 87 on a 4-pin relay are sometimes found. One line goes to the throttle switch and one goes into Fuse 6 to power the fuel pump and to activate the temperature sensing unit. Two lines come from Fuse 6 output—one goes to the pump; the other goes to the temperature sensing unit. If you test the wrong combination of wires at the relay and Fuse 6, or at the output side of Fuse 6 and the pump connector you will, of course, not get continuity. There is also a possibility of a broken wire in the circuit wiring or a defective relay.

Power to run the fuel pump in a K100 occurs when the ignition control unit (ICU) receives the starting signal. The signal is delivered when the ignition switch is turned to On, the starter button is pushed, and the engine is cranking. 12V should then delivered to the fuel pump connector to start the pump.

Here are two schematics downloadable from forum member frankenduck's comprehensive Brick information site. They can be enlarged until the relay terminal numbers—on the schematic that has them—can be read. 1   2 

There's at least even money on my having a correct understanding of what's happening on your side of things, or things in general.