Topic: Neutral Light comes on when I change gears

[boojiking]

My neutral light comes on on my 1976 Cb 400f whenever I disengage the clutch to change gears.

[lucky]

Just add a washer to the neutral light indicator.
Maybe the special washer is missing.

[scottly]

My neutral light comes on on my 1976 Cb 400f whenever I disengage the clutch to change gears.

This is probably due someone by-passing the Starter Motor Safety Unit (SMSU), which prevents the starter from working unless the clutch is pulled in, the trans is in neutral, or both. Honda replaced the SMSU, along with it's extra hardware, with a simple diode for later models. It's nothing to worry about...

[Bodi]

This is a problem with the starter safety system that allows electric start with the bike either in neutral or with the clutch pulled in.  There's no SMSU module on the 400F, just a diode - it's a small rectangular black thing with two terminals sticking out plugged into a socket in the electrical area, it looks sorta like a flasher.
Most likely the diode has failed and "gone short": if you remove it the neutral light will work properly. That assumes the wiring harness has not been modified - all bets are off if it has been.
What you'll lose by removing the diode is being able to use the electric start in neutral, but it will still work with the clutch pulled in.
To get back to normal you do need a diode in the socket. You can find the OEM part (there's a NOS one on ebay now and it may be available from Honda since the ebay one's label looks current) or just wire a diode (5A 100PIV would be good I think) to male 1/4" spade lugs and plug it in. One way will work properly, the other (wrong) way will probably act like it does for you now but it will not damage the diode.

[sopo400f]

Good info!