Topic: Neutral Light Won't Come On and Problems Ensue

[AtlTech]

So today I went to clean what seems to be about 40 years of gradually accumulated gunk from the area surrounding the chain and center stand of my 78' CB750F. While I was down there I figured, why not clean the chain as well and took care of that too. Finished up, let her bask in the sunshine of my driveway for a little bit, then came back out a couple hours later to go for a quick ride.

Imagine my surprise when I turned the key, put her into neutral, pressed the start button and heard a whole lotta nothin. Key is in, battery has 11.4 volts, but not a peep. I then noticed that my neutral light was not illuminated. Funny, it's definitely in neutral. Ok, so I was scrubbing down that way with some pretty potent chemicals, maybe I done goofed up the neutral switch. Went to pull it and dang, who decided that was a good place to put that mounting bolt? In the process of breaking the bolt loose, I also managed to snap the little mounting bracket off of the switch itself and to top it off, the switch still isn't coming out. Which brings me to the knowledgeable folks on this forum with a couple of questions;

Am I probably right in assuming the chemicals have disabled the neutral switch?
Does the mounting bolt double as a ground for the switch or am I fine with super gluing that bracket back onto the rest of the switch?
How in the blazes do I get the switch itself out of the crankcase?
Is there a way for me to bypass all this nonsense and just make the bike start whether it's in neutral or not?

[AtlTech]

One other thing to point out is that the bike has never started unless it is in neutral. Even with the clutch pulled in. I'm not sure if that's another issue, but either way, I'd like to be able to use my electric start.

[ekpent]

 Is the 11.4 volts for your battery a misprint ? If so that is pretty dead.  Losing the neutral switch should not disable the bike from starting though cannot say I have tried one disconnected. As for a broken one just plan on replacing it and when you find a used or new one and get a new oring gasket also. Depending on any interference from a muffler etc. they are easy to swap out.

[AtlTech]

Not a misprint on the 11.4. at least I don't think it is. PO had a voltage monitor permanently installed and that's what I'm going off of. It's usually read in the range of 11-12 and has started decently well since I've gotten it. At least the starter motor has been turning. This though, this is stone cold no start. I'm confident the disappearing neutral light and sudden issue are related.

[ekpent]

 May be having an effect on the starter circuit. Never tried one disconnected. You could quickly check for power at  the main fuse just to see if your getting any juice there. I think basically putting the wire to a ground with some clip on jumper will bypass the switch.

[Bodi]

The clutch switch connects ground directly to the solenoid on "diode" bikes, but the SSU I don't really understand and it may burn out in a way the clutch switch won't allow starting? I think th 78 model has the diode?
A blown diode disables neutral starting but the clutch switch will still let the starter motor run.
Confirm the clutch switch actually works (zero ohms with clutch disengaged), one wire is grounded,and the other connects to the solenoid or SSU.
You can bypass the whole safety system by connecting the solenoid wire that goes to red/black straight to ground.

[AtlTech]

So some follow up; I've checked resistance across the neutral switch and it seems to be operating just fine (aka: it had a small amount of resistance with the bike in neutral and 0 resistance otherwise). Likewise, the diode is giving me a solid reading with the multimeter. But I cannot for the life of me trace most of the other wires involved in this system. The harness is definitely not stock anymore and trying to figure out what colors have replaced what is gonna give me an aneurysm. On top of that, I'll be losing access to my garage in a few days so I'll need to make a repair decently quickly.

So, I also tried shorting the solenoid with a screwdriver. That worked just fine to get the motor turning, but the neutral light is still dead. Which is fine. I can live with that. So currently, the plan is to head to the hardware store for some extra wiring and a button and rig up a not-quite-permanent bypass of the solenoid until I can find out the original problem. I do want to keep looking for that original problem though so if you've got more suggestions or you think the bypass is a stupid idea, throw em at me.

[paulbaker1954]

The neutral switch is simply an earth point. There is a live feed that runs to both the oil pressure light and the neutral light. The connector is behind the headlight. If you have a multimeter check you are getting voltage at the connector. If not you have a wiring issue  before the connector. If you have voltage then check the bulb operation by running a bit of cable from the bulb output wire behind the headlight (just follow the colour) to battery negative. If that works then you have a wire problem from the back headlight connectorvto the neutral switch. This runs through the connector block behind the left hand panel then on to the neutral switch.

I had a similar problem with my oil light switch that I found was the connector block behind the left hand panel had come loose.



Obvious question have you checked the

Get hold of the wiring diagram and test each bit logically it's a very simple circuit 12v feed to bulb and finally neutral switch earths it to light the bulb

By the way the battery voltage has nothing to do with it even 9 v will light the bulb at 11 odd volts you have a knackered battery but that's another issue

Good luck

[beemerbum]

Do I understand correctly That The neutral switch under the motor can be replaced on a '77 K7 750 without taking off the stock exhaust or pulling the motor? Arthritis prevents getting underneath for a look. We get old too soon and smart too late.