any suggestion on where I go from here? Something is keeping the fuel pump from working, but damn if I know what.
Have you verified the operation of the pump independently of the rest of the bike's wiring? Disconnect the tank from the harness and apply 12V to the pins on the tank connector corresponding to the pump - Green/White and Brown.
- Does the pump operate? If yes, good. If not, check wiring.
after switching on ignition, I get no voltage at female green/white on connector.
You'll want to check the sources of power for the components of interest for getting the fuel pump to operate. Those components are Motronic unit, Motronic relay, Fuel Pump relay. From my documentation for a 1994 K1100LT, fuses of interest are:
Fuse 6 = Battery (Unswitched) = Fuel Pump Relay(30)
Fuse 5 = Battery (Unswitched) = Motronic(15), Motronic Relay(30)
Since these are unswitched circuits, power should be present on those pins with our without the ignition key being switched on.
- Are you reading battery voltage on the Fuel Pump Relay pin 30 (Red/Green) wire (relative to ground)? If yes, good, If not, check wiring for broken wires or loose connections.
- Are you reading battery voltage on the Motronic pins (Red/Yellow) at the Motronic and the Motronic relay? If yes, good, If not, check wiring for broken wires or loose connections.
Now that you've verified that power is being provided and that your pump is capable of running, you need to check whether it is getting switched on correctly. Power at pin 30 of the fuel pump relay will supply the power to the tank connector. If you don't read voltage at the fuel tank connector harness side when you switch on the ignition, start tracing power to the fuel pump relay coil. It starts at the ignition switch, travels through the side stand switch, through the fuel pump relay coil and finally to the Motronic switched ground lead.
- Are you reading battery voltage on Pin 15 of the ignition switch (Green) when the key is turned on? If yes, good, If not, check the ignition switch.
- Are you reading battery voltage at pin 85 (green/yellow) of the fuel pump relay with the side stand up? Does voltage drop to zero when the side stand is down? Do you get the exact same behaviour at the Motronic relay pin 86 (Green/Yellow) when you raise and lower the side stand. If yes, good. If not, check the side stand switch and the associated wiring.
The last piece in this puzzle is the Motronic switched ground (Blue/Brown). The Motronic controls the ground to the fuel pump and turns it on or off depending on other sensors on the bike.
- for test purposes only to isolate the Motronic, you can temporarily ground the Blue/Brown wire on the fuel pump relay. That way it does not depend on the signal from the Motronic. Be prepared. When you turn on the ignition and the side stand is up, the fuel pump should start working if all the other tests above passed. If it does, it means the Motronic is not switching the ground for some reason. You'll have to continue troubleshooting that problem. If the pump fails to run even with this temporary ground in place, then the fuel pump relay is bad. Get a new one..
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