I am redoing the wiring on my 1992 NC31 CB400. The previous owners made a mess of the harness while importing bits from another bike's harness. Lots of ghastly Frankenstein soldering made it work somehow but the battery would drain every day for some reason. So I elected to redo the harness. Don't be like me.

Anyway I discovered a fuel cut relay somewhere in the tangle. It's labelled Shindengen and numbered TF306. The bike has no fuel pump, or I don't know where to find it. I'm seriously considering cutting out the fuel cut relay entirely but a blue/yellow wire leads out from it and branches off to the left coil on one hand and the TCI box on the other. Seems important.

I seriously believe the fuel cut relay only got in there because an entire harness was transplanted wholesale into the early model NC31 from a later CB400 model.

Can I safely omit the fuel cut relay from the harness? Is it useful without a fuel pump? What does it do?

Of course there is no fuel pump in NC31. Probably your harness is from another bike. You can cut it out but keep in mind not to loose any continuity with any other part.

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I suspect that the fuel cut relay removes power from the fuel pump if the engine is not running. The engine running signal is provided by the wire from the ignition coil and TCI. No fuel pump means no need for the relay. You should be able to remove the relay without affecting the engine running.

panossp25 wrote: Thu Jul 01, 2021 4:58 am Of course there is no fuel pump in NC31. Probably your harness is from another bike. You can cut it out but keep in mind not to loose any continuity with any other part.

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Thank you panossp25. I have just cut out the fuel cut relay keeping everything else intact. The harness is still sprawled out across my living room floor right now as I iron out other strange innovations in it. Can't promise updates any time soon but you have brought me one step closer to completing my project.

magg wrote: Thu Jul 01, 2021 5:15 am I suspect that the fuel cut relay removes power from the fuel pump if the engine is not running. The engine running signal is provided by the wire from the ignition coil and TCI. No fuel pump means no need for the relay. You should be able to remove the relay without affecting the engine running.

Thank you magg for confirming my suspicions. I just wasn't certain if there was a fuel pump or not. The engine was cutting out randomly while riding but my research leads me to check the carbs and the fuel lines/filters/tank air vents/starter relay and even reg/rec. Anyway your response gives me that much confidence to go ahead. Already cut out the relay.