Topic: Neutral light - not going out

[Radski]

I installed a DCC mini speedo when I was mocking my bike up. Got it running and IIRC the neutral light was functioning perfect upon the prelim wiring.

Now that i took it all apart, cleaned it all up and got it all back together, my neutral light is constantly on and wont turn off when the bike is in gear. Checked the wiring and it appears to be as it should. 

Question... its a '76 CB750K and I have two wires in the harness that are both green with red stripes. One a lighter green that appears to attach at the bottom of the engine, and the darker one I've found in the left control loom (clutch switch?) and back at the starter solenoid. The picture I took of the wiring when I first did it (which I should have done more and more angles) appears the light green is just open (not connected) coming out of the main harness. The darker is attached from the controls to the main harness. BUUUUT in the schematics I only see one green wire with a red stripe! what gives!?

Obviously not a big deal but I'd like to get the light in the headlight working properly and turning off when in gear. Anyone have any ideas or suggestions?

[BenelliSEI]

Your neutral wire is sending a ground from the switch, when in neutral. The light socket should have power all the time. First check if the ground circuit opens when you shift into gear. Start at the neutral switch (with the wire off). If it opens there, how about at the light? Is the wire pinched somewhere along the way, and permanently grounded? Maybe the lamp socket is getting a permanent ground from the way it is mounted in the housing?

[Radski]

So I think I have it figured out but I have no idea what to do.

The lime green/red wire that goes from the actual switch under the engine, I found the other end that comes out of the wiring harness where normally it would connect and be stuffed in the headlight. THIS end is not plugged into anything.

BUT I have no idea where to plug it into. There is no matching wire, especially since I'm using the DCC mini speedo which has a ton of wires.

Back to the wiring vs. schematic issue from my first post.... on a '78 750K wiring diagram it shows that the lime green/red stripe and dark green/red stripe circuit together. So I'm going to assume that the '77 is the same?

I actually plugged the lime green open end into a double that ties the dark green/red stripe wires together from the clutch and main wiring harness...and still no luck.

Any suggestions from this description?

[BenelliSEI]

Electrical issues are frustrating to solve and the explanation can be the same. Try and think of the problem in isolation..... The switch under the engine is sending a ground to your lamp. It should only do that when you are in Neutral. Check that first. Hook a 12V. test light to the + terminal on your battery. Now touch it to the end on the red/ green wire end. You should get a light in neutral, and it should go out when you select a gear?

Assuming that works, now think about the bulb socket. It needs two wires: power and ground. The ground is switched on and off, by the neutral switch wire. The power should be on whenever you switch on your key. Hook your test light to the - terminal on the battery and test that lamp socket wire? If you have power and ground, the bulb should work?

Now if the bulb stays lit all the time, WHY? If the ground wire is switched off (and you are in a gear), then the lamp socket is getting a ground from where? Is it grounding in the housing? Is it faulty. Think it through....... good luck.

[Radski]

Electrical issues are frustrating to solve and the explanation can be the same. Try and think of the problem in isolation..... The switch under the engine is sending a ground to your lamp. It should only do that when you are in Neutral. Check that first. Hook a 12V. test light to the + terminal on your battery. Now touch it to the end on the red/ green wire end. You should get a light in neutral, and it should go out when you select a gear?

Assuming that works, now think about the bulb socket. It needs two wires: power and ground. The ground is switched on and off, by the neutral switch wire. The power should be on whenever you switch on your key. Hook your test light to the - terminal on the battery and test that lamp socket wire? If you have power and ground, the bulb should work?

Now if the bulb stays lit all the time, WHY? If the ground wire is switched off (and you are in a gear), then the lamp socket is getting a ground from where? Is it grounding in the housing? Is it faulty. Think it through....... good luck.

Such a great explanation! Thank you. I'll try some of this out later today when I can. Will be in touch.

[Bodi]

I think this bike should have come with some sort of starter safety system so you can use the electric starter in neutral or with the clutch disengaged, but not in gear with clutch engaged. That may have been removed.
For simple wiring bypassing any safety system: you must have found the neutral light wires. If this is an LED you will need to watch polarity - it won't light with polarity reversed but no damage is done that way.
One wire from the neutral lamp goes to switched power, any black wire.
The other wire goes to the wire from the neutral switch. In neutral, the switch grounds that wire completing the lamp circuit.
If your digital dashboard expects a switched power for the neutral light and has no way to change that, you're either screwed... or need to add something like a relay to make it work.
You can check the neutral switch with a test light or Ohm meter - it should close to ground in neutral, with no connection to ground in gear. There is no way to change/rewire/modify it to switch battery power rather than ground.
Starter function with modified harness:
The usual way to remove the safety diode or module is to directly ground one wire to the starter solenoid coil, the other solenoid coil wire is switched battery power from the starter switch. Just try not to start it in gear.
With the diode removed or blown open and wiring unmodified, you can start with clutch pulled in but not just in neutral. Not sure what happens with a removed/blown starter safety module but I believe those were gone by 77 and replaced by the diode?

[Radski]

Electrical issues are frustrating to solve and the explanation can be the same. Try and think of the problem in isolation..... The switch under the engine is sending a ground to your lamp. It should only do that when you are in Neutral. Check that first. Hook a 12V. test light to the + terminal on your battery. Now touch it to the end on the red/ green wire end. You should get a light in neutral, and it should go out when you select a gear?

Assuming that works, now think about the bulb socket. It needs two wires: power and ground. The ground is switched on and off, by the neutral switch wire. The power should be on whenever you switch on your key. Hook your test light to the - terminal on the battery and test that lamp socket wire? If you have power and ground, the bulb should work?

Now if the bulb stays lit all the time, WHY? If the ground wire is switched off (and you are in a gear), then the lamp socket is getting a ground from where? Is it grounding in the housing? Is it faulty. Think it through....... good luck.

Ok...hooked the voltmeter to the battery + side and the end of the wire in question. I confirmed that when I touched the end of the wire with the voltmeter lead, then shifted into gear, the voltmeter cut nearly to zero. So therefore that would lead me to believe that the switch is operating correctly.

The problem lies I believe in the connection (or in this case lack thereof) between the lime green/red to the speedometer. The mini speedos diagram shows to wires for the neutral light (bulb). A green which it says is the power, and a green/black that is the negative. The green is connected to a black in the harness (+) and the green/black is in a green from the harness (ground/ -)

What I know is happening is that I dont have the connection from the switch (lime green/red wire in question) to the speedo. My problem is I dont know where to plug it into. I tried touching the lime wire in question to the power or positive green wire of the speedo and got nothing. I also plugged the wire in question into the dark green/red stripe connection which should be the clutch switch to the main harness...and nothing. I also dont remember in the original headlight how this connection was made.

Any other suggestions? I did try the lime green/red into a ground and it also did not change anything.

Im lost.

[RAFster122s]

Shouldn't your green red from the bike's neutral switch should connect to the Speedo's green black wire? It is providing the ground path through the neutral switch for the indicator bulb.


If you have connected the Speedo's green wire they indicate needs power to a black wire you are feeding it switched power. Then you are grounding the green black wire completing a ground path for the indicator bulb constantly...your neutral switch is not wired to the speedo then...

[Radski]

ok Benelli...you're the man.

After I posted my last rant, i re-read your posts and it finally got to me. Took some time (obviously) but I figured it out with your help.

The negative from the speedo needed to be plugged into the wire in question, the open lime/red. Previously as you read in my rant, that negative was plugged into a permanent ground from the harness. I changed the connector so the two wires would connect, and viola!!

IT WORKS!!!

thank you thank you thank you for your descriptions. It paid off!

[BenelliSEI]

Good news! And congrats!