Topic: CB400f voltage loss between battery and pretty much everything?

[Deltarider]

[...]
V2 (measured across the "drive" (low beam) and ground connectors on the headlight socket): -0.002v (doesn't make sense!)
[...]
V2 (measured across the "pass" (high beam) and ground connectors on the headlight socket): -0.03v (doesn't make sense!) [...]

You did it right and I agree the outcome of the V2 doesn't make sense. With such ultra low voltage across the positive side and the negative side of the lamp there's no light possible. How in the world can that bulb emit light when... there is no power?

[Tenn_CB400f]

[...]
V2 (measured across the "drive" (low beam) and ground connectors on the headlight socket): -0.002v (doesn't make sense!)
[...]
V2 (measured across the "pass" (high beam) and ground connectors on the headlight socket): -0.03v (doesn't make sense!) [...]

You did it right and I agree the outcome of the V2 doesn't make sense. With such ultra low voltage across the positive side and the negative side of the lamp there's no light possible. How in the world can that bulb emit light when... there is no power?

I thought so too, but I did a little bench test with a battery and a couple of headlamps, one the oem Stanley from the CB400f, and a repeat with a Hella H4 headlamp I have been saving for this bike. I get the same results as I did on the bike for V2.

[Deltarider]

I am not familiar with your model's layout of the switch unit on the handlebar's left hand side. Besides the dimmer switch and the one for the blinkers, does your horn button have two functions: push = horn, slide to the right = to flash headlight, usually marked PA like the models for Europe had? See pic of mine. If so, are you sure that slide function is still OK, meaning when slided to the right, the knob will return (by its spring) as soon it's released? When it's lame (like on my bike), there's a chance both filaments in the headlamp bulb will receive power.
But... according to my information, US models are not supposed to have this PA function, so if yours has it, either your bike is a European model or the switch unit is not the original for your bike and... its wiring.
Another question. When you temporarily remove the headlamp's fuse, does this 'cure' (= brighten up) the other consumers like the blinkers?
Last question. Are you aware that around idle these bikes will not show much voltage as the battery will not receive charge unless over 2000 rpm and so will actually drain power?

[Tenn_CB400f]

I am not familiar with your model's layout of the switch unit on the handlebar's left hand side. Besides the dimmer switch and the one for the blinkers, does your horn button have two functions: push = horn, slide to the right = to flash headlight, usually marked PA like the models for Europe had? See pic of mine. If so, are you sure that slide function is still OK, meaning when slided to the right, the knob will return (by its spring) as soon it's released? When it's lame (like on my bike), there's a chance both filaments in the headlamp bulb will receive power.
But... according to my information, US models are not supposed to have this PA function, so if yours has it, either your bike is a European model or the switch unit is not the original for your bike and... its wiring.
Another question. When you temporarily remove the headlamp's fuse, does this 'cure' (= brighten up) the other consumers like the blinkers?
Last question. Are you aware that around idle these bikes will not show much voltage as the battery will not receive charge unless over 2000 rpm and so will actually drain power?

1: My switch is DOT, and doesn't have a flash function or any other buttons on the front:



Here's the wiring bundle for the switch:



2: I'll try that

3: Yes I am aware. I am doing this testing with the motor off, but I am keeping the (new) battery hot in between tests. I do not see that both filaments are lit simultaneously, despite seeing some volts at the opposite hi/lo setting when one is on.

[scottly]

Excuse me, I got lost as soon as you started claiming a voltage drop on the positive side of the circuit was due to a problem in the negative/ground side of the circuit?? Just what is this V4 measurement?

Scottly, the V4-measurement procedure is in reply#3. Every automotive mechanic here is supposed to have learned this and where needed practise it.

Really?? I have never heard of a "V4 measurement procedure" in all of my automotive classes, nor in all of my electronics classes.

[scottly]

That means you are dropping 1V through the switch itself. Have you measured the drop at the red and black wires at the ignition switch since you replaced the fuse box?

[Deltarider]

Excuse me, I got lost as soon as you started claiming a voltage drop on the positive side of the circuit was due to a problem in the negative/ground side of the circuit?? Just what is this V4 measurement?

Scottly, the V4-measurement procedure is in reply#3. Every automotive mechanic here is supposed to have learned this and where needed practise it.

Really?? I have never heard of a "V4 measurement procedure" in all of my automotive classes, nor in all of my electronics classes.

Well, you are never too old, are you  . The V-4 measurement is quite old school actually. Nowadays you plug a modern vehicle to a laptop and an app will spew out the data and can make the diagnosis for you.
Tenn's problem seems to be a tough one. I am not particularly familiar with the special wiring scheme of models for the US.
I agree the usual suspects are: fuse and fuseclips, the key IGN switch, and - as far as US models - the starter switch.The latter has to endure quite some amps, whenever the key IGN switch is switched to ON due to that silly headlamp-always-on arrangement Honda had been forced to by US geniuses. CB400Fs for other markets didn't have that nonsense and I don't know if Honda has realised the possible premature wear of the contacts on US models.
In the NEG path the usual suspects are: the connection of the battery NEG cable to the frame, a loose and/or corroded connection of that thick green wire in the vicinity of the coils and/or other corroded connections to GND.
The results of Tenn's measuring led me to conclude the resistance is in the negative path. But... he has some funny readings besides, concerning the headlight bulb. I wonder what your opinion is on that. What we don't know, is if someone has messed with the wiring before. In the headlamp bucket a mistake is easily made.
A possibility for diagnosis remains: disconnect the battery, switch the DMM to LOW OHMS and try to locate the resistance, step by step. Not my favorite, but...

[scottly]

Low beam:


V4 (measured across the - battery terminal and the ground wire on the HL socket): 0.192v


High beam:


V4 (measured across the - battery terminal and the ground wire on the HL socket): 0.222v

ugh

I also re-checked the green ground wire just behind the airbox against the battery minus, key and HL on, and get 0.010v.

The voltage drop from the battery negative terminal and the green wire grounds is well within acceptable limits, and is not the issue with the 3-4 volt drop from the battery plus terminal to the headlight, no matter what Delta says.

[Deltarider]

Delta just interpreted the results Tenn communicated at first. The fourth of the V-4 measurement is supposed to measure a possible Vdrop between the minus side of the consumer and the Batt minus terminal. If Tenn reported a considerable Vdrop in that path of no less than 4,9V and the Vdrop in the positive path was a negligible 0,219, I conclude the resistance is in the minus route. It's very simple logic. I depend on Tenn's reporting. How would you, Scottly, then have interpreted his results in reply #21.
When now the Vdrop appears to be in the positive path, do the Vdrop measuring in that route: first Batt+ to that dim light and then with the black probe from that dim light a step back in the route towards the battery and another and another until you read say 0,5 V maximum. Consult the wiring diagram for your model. It will show you the connections. You can stop where you read 0,5V max. Up to that point the line is good, so the resistance is in the very next part of the route towards the bulb. Simple.

[Ozzybud]

I also noticed by accident that when the high beam is on, the lo beam gets about 4v, and when the low beam is on, the high beam gets similar?

Is the headlight still dim? I think you mentioned that it had always been dimmer than normal? Exactly how did you measure the voltage; was it with one meter lead connected to the battery - terminal and the other meter lead probing the white and blue wires at the back of the headlight?

Ignition switch on, lo-beam on. Red probe on the + battery terminal, black probe on the "main" connector in the headlight plug = 12.1v.

Ignition switch on, lo-beam on. Red probe on the + battery terminal, black probe on the "pass" connector in the headlight plug = 4.0v.

Ignition switch on, hi-beam on. Red probe on the + battery terminal, black probe on the "pass" connector in the headlight plug = 12.1v.

Ignition switch on, hi-beam on. Red probe on the + battery terminal, black probe on the "main" connector in the headlight plug = 3.95v.

Headlight maybe is less dim but still not really bright.

So the fusebox swap seems to have done something.

Seems as if The problem is fixed with the fuse block replacement.

He has over 12V going to the headlight now

[Deltarider]

Seems as if The problem is fixed.
He has over 12V going to the headlight now

I also noticed by accident that when the high beam is on, the lo beam gets about 4v, and when the low beam is on, the high beam gets similar?
Ignition switch on, lo-beam on. Red probe on the + battery terminal, black probe on the "pass" connector in the headlight plug = 4.0v
Ignition switch on, hi-beam on. Red probe on the + battery terminal, black probe on the "main" connector in the headlight plug = 3.95v.

What is this ^ then?

[Ozzybud]

Seems as if The problem is fixed.
He has over 12V going to the headlight now

I also noticed by accident that when the high beam is on, the lo beam gets about 4v, and when the low beam is on, the high beam gets similar?
Ignition switch on, lo-beam on. Red probe on the + battery terminal, black probe on the "pass" connector in the headlight plug = 4.0v
Ignition switch on, hi-beam on. Red probe on the + battery terminal, black probe on the "main" connector in the headlight plug = 3.95v.

What is this ^ then?

It doesn't seem to be affecting operation.

[Tenn_CB400f]

That means you are dropping 1V through the switch itself. Have you measured the drop at the red and black wires at the ignition switch since you replaced the fuse box?

Here's what I get at the ignition switch wires with the key on (low beam) following the new fuse block installation.

This is just voltage (+ probe on the positive battery terminal and the - probe on the wire in the ignition switch connector.

I don't really understand why I am getting the readings I am at the headlight socket when attempting to do the V4 test, but the headlight seems a little brighter and I am getting much closer to 12V to the bulbs when I just check voltage at the headlight socket.

My next step will be to hose down the switches with switch/contact cleaner, then put it all back together and run the bike and see how it acts.

I really appreciate all the help!

[scottly]

I got fouled up in that V4 testing and couldn't quite understand a difference in V2 and V3.

Yeah, I know.

[scottly]

I don't really understand why I am getting the readings I am at the headlight socket when attempting to do the V4 test, but the headlight seems a little brighter and I am getting much closer to 12V to the bulbs when I just check voltage at the headlight socket.

When you are reading 4V on one of the headlight leads, with one of the meter leads connected to the battery + terminal, you are reading the voltage drop in the positive side of the circuit on the filament that is lit, and if you check the other wire, you will read battery voltage through the unlit filament, just like if you checked the voltage from battery + to ground. As far as which is high beam and which is low beam, the blue wire should be the high beam. You reported that the "pass" wire had a slightly greater drop, which suggests that it is the high beam, due to the greater current draw.
In any case, it appears that there are small voltage drops at every stage, that add up. You might want to clean all of the connections in the harness. If all else fails, you could use relays to bypass the stock harness, but that's a last resort.

[Deltarider]

I got fouled up in that V4 testing and couldn't quite understand a difference in V2 and V3.

Yeah, I know.

I feel sorry you have difficulties in applying the V-4 method. It's a very simple and basic disciplin to diagnose and - in the process - safeguard you from overlooking the unexpected. It's also an universal method, practised by mecs the world over. Here's an anecdote that illustrates the 'unexpected'.
My old comrade in California had owned an old Triumph sportscar. I have forgotten what the actual issue was. Anywy, he could not understand what he was doing wrong in trying to diagnose and solve the problem. Turned out his old car was of the old British generation that still had the chassis as the positive...
I myself have located and solved quite a few 'bad grounds' on cars as well as bikes. With my explanation, I don't see the problem. I'm sorry, but I cannot make it any clearer than I did.

[Tenn_CB400f]

I got fouled up in that V4 testing and couldn't quite understand a difference in V2 and V3.

Yeah, I know.

I feel sorry you have difficulties in applying the V-4 method. It's a very simple and basic disciplin to diagnose and - in the process - safeguard you from overlooking the unexpected. It's also an universal method, practised by mecs the world over. Here's an anecdote that illustrates the 'unexpected'.
My old comrade in California had owned an old Triumph sportscar. I have forgotten what the actual issue was. Anywy, he could not understand what he was doing wrong in trying to diagnose and solve the problem. Turned out his old car was of the old British generation that still had the chassis as the positive...
I myself have located and solved quite a few 'bad grounds' on cars as well as bikes. With my explanation, I don't see the problem. I'm sorry, but I cannot make it any clearer than I did.

I understand the concept, just not the results I got, which led me to believe I was performing the test incorrectly. Where would you measure the V2 test on the low-beam of the headlight?

[Deltarider]

V2 measures the potential in a live circuit over both sides of the part that does not perform 100%, so the red probe where the white wire connects the bulb and the black probe on the green wire as close as possible to the bulb. Better even the side of the metal part of the bulb, but I'm not sure you can reach it on a US model. You may want to consult the far left of the US model wiring diagram: http://manuals.sohc4.net/cb400/technical_reference/WD40077.jpg
Tip! Right after this, don't switch anything off and measure the volts at the battery's plus and minus terminal. I bet the outcomes will be much closer now. Here's why. Our bikes have a very small battery. When you measure the battery's potential with everything OFF, it's higher than with the ignition and consumers switched ON. Where with everything OFF, you can read 12,6V or more, with things ON and without the engine running, you could see 1 -1¹/₂ volts less. So also your reference V1 across the battery terminals should always be measured with things ON.

[scottly]

OK, after sorting through all the nonsense, here is a breakdown of the voltage drops through the wiring to the headlight. All measurements are from the battery + terminal to the test points, which eliminates any drop in the negative, or ground side of the circuit.

At the black wire of the ignition switch (the output) the drop is 1.202V, while with the old fuse box measured 1.8V. There is still some resistance between the red wire and the battery + terminal. (The ignition switch itself has already been ruled out.)
Between the ignition switch and the black supply wire at the start switch, there is only a .1 volt additional drop, or 1.3V. The drop at the black/red wire on the output side of the start switch is 2.3V. By the time the power goes through the headlight fuse and back to the dimmer switch on the black/yellow wire, the drop has increased to 3.3V, and that goes to 4V at the headlight. There is no single connection problem, but several that add up.
BTW, I dug a 400 harness out of a box today and checked the headlight socket: "pass" is the low beam, and "drive" is the high beam.

[Tenn_CB400f]

Thank you!

 

I'll show myself out.

I know we should never assume, but here's why I assumed "pass" was hi beam:

[bryanj]

From that list sounds like a big can of contact cleaner, a medium roll of wet n dry paper, dielectric grease tiny round wire brushes and days of time will cure it.

[Tenn_CB400f]

Would you look at this little thing! All the headlight juice flows through there. I'm definitely adding a relay!

[Deltarider]

Mwah... when I calculate 60 Watts for high beam and maybe 4 Watts for a Ba9s pilot light it might have, you're looking at a little over 5A. The only relay I have on mine is for the Voxbell horns, but they draw 10A and needed an extra 15A fuse.