Problems getting bike up and running. Narrowed it down to ground from ecu to pin 85 on fi relay. Have continuity on the wire from pin 7 of ecu to pin 85 of the relay, but when I try to start it, it is getting voltage from somewhere. I can run a wire from ground to back of relay and it will start. Does anyone know where i might be losing this ground from the ecu or will i just have to replace the ecu? sorry did not mention what bike. It is  1985 K100rt.

if the pin going to the ecu is lossy or the cable has some resistance
you will see voltage on the negative side of the relay after the start process has been initiated ...other wise with power on there should be positive on the earth side as well ...its when the ecu switches on ( to ground ) that the voltage drops

might be worthwhile doing 2 things

take the connector off ...and clean up both contacts ...(ie  the connector strip to the ecu pins ....and the socket side as well )

 make sure that there is a good earth to the ecu from the frame ground  by the mounting bolts
....near the ecu itself there is a bolt through  the frame ....with several lugs under that bolt ...clean it all up

some folks have done this but missed at least one lug under the bolt

btw make sure that the ground cable from the battery to the gearbox mount is clean and good contact ....highly recommended to upgrade this cable as well to at least 8mm

Since Hall Effect sensors usually go out gradually, my guess is that it's either the ICU (called that on a K because it only controls the ignition while the L-Jetronic controls other engine management functions) or the yellow/brown wire from the ICU to the relay is faulty.

First check that you have good continuity from Pin 7 on the ICU connector to the yellow/brown wire to the FI relay to see if the wire's good.

If it's not that then I'd guess that the ICU has gone bad.

Thanks, will pull grounds and clean them all good and retighten. have tested the wire from the pin of ecu to the relay and show good continuity there.

Used ICU units are readily available too.