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

[Ozzybud]

 connect the + meter lead to the battery + terminal, and then check the voltage with the other meter lead at the red wire on the ignition switch with the key on.

Do this test and report back.

Mine is 0.83 volts to the red
2.97 to the black.

So the loss is in  the switch?

[scottly]

 connect the + meter lead to the battery + terminal, and then check the voltage with the other meter lead at the red wire on the ignition switch with the key on.

Do this test and report back.

Mine is 0.83 volts

You are still dropping .83 volts through the harness/fuse block, but not quite a smoking gun. What do you read at the black wire at the ignition switch with the meter connected the same way?

[Ozzybud]

2.97 to the black
I edited the post after you replied

[scottly]

 connect the + meter lead to the battery + terminal, and then check the voltage with the other meter lead at the red wire on the ignition switch with the key on.

Do this test and report back.

Mine is 0.83 volts to the red
2.97 to the black.

So the loss is in  the switch?

Missed your edit Yes, your switch is responsible for a 2.14 volt drop, which is a smoking gun!

[Ozzybud]

 connect the + meter lead to the battery + terminal, and then check the voltage with the other meter lead at the red wire on the ignition switch with the key on.

Do this test and report back.

Mine is 0.83 volts to the red
2.97 to the black.

So the loss is in  the switch?

Missed your edit Yes, your switch is responsible for a 2.14 volt drop, which is a smoking gun!

I believe it is a newish reproduction. During my restoration it and the key looked brand new. Is this common for the repos to go bad? Or bad when new?

[scottly]

I have heard of Emgo(?) brand ignition switches that didn't hold up well.

[bryanj]

Back in the 70's fitted lots of emgo parts here in uk with no problems also daichi ponts but quality seems to have dropped of, or they are made elsewhere

[Deltarider]

Thanks again everybody for suggestions.

I first tried the V-4 measurement on the headlight, and I think I did it right and got the below results, which seem bad. I also tested the voltage at the various ignition switch connections and recorded them. I took the switch apart and inspected and cleaned everything and reassembled and got about the same, so I doubt it's the switch. It was in excellent shape inside.

(off ignition should be 12.9V)



I checked the wires and connections inside the headlight bucket for the running light/turn signals in the front and was chasing grounds, and the signal wires don't match the diagram (Clymer manual) in that both signals have two black wires with little tracer rings at the terminal.

There are quite a few green-wire female connectors in the headlight bucket with two empty connections, so I just need to trace a few. No visible signs of hackery (which would have been from me!).

One comment earlier suggested setting my meter on 2v to test for leakage:

"Set your meter to 2V and see if you can detect any V-drop:
1) Between Batt + and where it connects to the fuse box. Usually there is no V-drop here, but... disciplin.
2) Over the fuse itself. This can be the case. Clean contacts and check again.
3) Between fuse and IGN key switch.
4) Between IGN key switch and black wiring in the headlamp bucket."


Is there a way to set my meter to 2V?

Like I said, thank you everyone.

Ten, looking at the results of your measurement, it seems the voltage drop is in the NEG route. My first step would be to inspect the connection of the thick cable that runs from the Batt minus to the frame. You can disconnect the cable from the frame for a close inspection. Is there any rust? Has the frame been painted/powder coated so that now the paint hinders the flow of electrons. Clean the ring connection and use some sandpaper to clean the eye well. Is the other end of the cable connected well to the Batt minus terminal? Also here it may need some cleaning. This is the first step. Hope this will cure the issue.
If your meter does not have a 2V position, it's no problem. Just use the position your meter has.

[Tenn_CB400f]

 connect the + meter lead to the battery + terminal, and then check the voltage with the other meter lead at the red wire on the ignition switch with the key on.

Do this test and report back.

Mine came out to 1.85v to the red wire, switch on.

[scottly]

Tenn, now check at the black wire.

[Tenn_CB400f]

Thanks again everybody for suggestions.

I first tried the V-4 measurement on the headlight, and I think I did it right and got the below results, which seem bad. I also tested the voltage at the various ignition switch connections and recorded them. I took the switch apart and inspected and cleaned everything and reassembled and got about the same, so I doubt it's the switch. It was in excellent shape inside.

(off ignition should be 12.9V)



I checked the wires and connections inside the headlight bucket for the running light/turn signals in the front and was chasing grounds, and the signal wires don't match the diagram (Clymer manual) in that both signals have two black wires with little tracer rings at the terminal.

There are quite a few green-wire female connectors in the headlight bucket with two empty connections, so I just need to trace a few. No visible signs of hackery (which would have been from me!).

One comment earlier suggested setting my meter on 2v to test for leakage:

"Set your meter to 2V and see if you can detect any V-drop:
1) Between Batt + and where it connects to the fuse box. Usually there is no V-drop here, but... disciplin.
2) Over the fuse itself. This can be the case. Clean contacts and check again.
3) Between fuse and IGN key switch.
4) Between IGN key switch and black wiring in the headlamp bucket."


Is there a way to set my meter to 2V?

Like I said, thank you everyone.

Ten, looking at the results of your measurement, it seems the voltage drop is in the NEG route. My first step would be to inspect the connection of the thick cable that runs from the Batt minus to the frame. You can disconnect the cable from the frame for a close inspection. Is there any rust? Has the frame been painted/powder coated so that now the paint hinders the flow of electrons. Clean the ring connection and use some sandpaper to clean the eye well. Is the other end of the cable connected well to the Batt minus terminal? Also here it may need some cleaning. This is the first step. Hope this will cure the issue.
If your meter does not have a 2V position, it's no problem. Just use the position your meter has.

You mean this connection, at the rear motor mount bolt?



AFAIK that nut has never been loosened, and the frame paint is from 1975. I took it apart, steel-wooled and retightened, but it didn't seem to make a change. Battery end is clean and tidy, having just been attached to the new battery.

Thanks!

[Tenn_CB400f]

Tenn, now check at the black wire.

1.825v on the black wire at the switch, key on

[scottly]

That means your switch is OK. Now you need to find where the 1.85V drop on the red wire is coming from. The red wire goes back from the ignition switch to the main 15 amp fuse, and then from the fuse to the battery + connection, which is usually on the large bolt on the starter solenoid. Once again, the most likely suspect is the fuse box. Probe each side of the main fuse and report back.

[Tenn_CB400f]

That means your switch is OK. Now you need to find where the 1.85V drop on the red wire is coming from. The red wire goes back from the ignition switch to the main 15 amp fuse, and then from the fuse to the battery + connection, which is usually on the large bolt on the starter solenoid. Once again, the most likely suspect is the fuse box. Probe each side of the main fuse and report back.

On it! I really appreciate the help.

[Tenn_CB400f]

That means your switch is OK. Now you need to find where the 1.85V drop on the red wire is coming from. The red wire goes back from the ignition switch to the main 15 amp fuse, and then from the fuse to the battery + connection, which is usually on the large bolt on the starter solenoid. Once again, the most likely suspect is the fuse box. Probe each side of the main fuse and report back.

The same measurements on the fusebox are:

Main (15A) "rear" connection: 0.98v
Main (15A) front connection: 0.90v

15A fuse was kinda hot!

Head (7A) rear connection: 3.48v
Head (7A) front connection: 3.44v

Tail (7A) rear connection: 2.1v
Tail (7A) front connection: 2.1v

[bryanj]

That fusebox needs replacing

[Tenn_CB400f]

That fusebox needs replacing

View under the cover in back:



The picture makes the MAIN fuse connectors look less scorched than they are.

Anyone make a blade-fuse replacement? We had to do this with those euro fuses in a Guzzi once.

Appreciate the help!

[denward17]

^HondaMan probably does (Mark Parish)

Link to website: www.SOHC4shop.com

I have 2 of the blade style from Mark installed on a 550 and 750, they work well.

[scottly]

You might try cleaning the fuse holder clips with a .22 caliber bore brush, if you have one handy. Are the clips tight on the fuses?

[scottly]

Head (7A) rear connection: 3.48v
Head (7A) front connection: 3.44v

You may have other problems with the headlight, besides the fuse box. The feed for the headlight goes through the starter switch. When at rest, The black wire is connected to the headlight black/red wire. When the start button is pressed, the black wire is switched to the red/yellow(?) wire to operate the starter.

[Ozzybud]

I tested my fuse holder . And my readings were almost identical to tenns numbers. But yesterday my switch readings pointed to a bad switch. This was after completely disassembling the fuse holder and re'-soldering the bad connections. I have a NOS fuse holder on the way. I don't believe it will change anything If the fuse holder is getting hot there is resistance there and likely a poor connection

[Deltarider]

If the result of the 4th of your V4 measurement - a 4,9 V drop! - concerned indeed the NEG route, then there is the problem.
Looking at your pic, I still don't know what to think of your minus cable. Near the connection to the engine, the copper looks quite corroded. For a simple test you could temporarily add an extra parallel wire from the Batt minus terminal to the engine or unpainted part of the frame and see if it improves the brightness of the lights. It's a simple test and there's no risk.
If there's no improvement, you'll have to find where then in the green (= negative) route is a resistance that causes the V drop.
Then my first step would be to check the green connection to the frame near the coils. It's quite a thick wire. Is it still there? Is the connection sound or maybe corroded? See pic below.

[Ozzybud]

A little perplexed.... but I am going to ride with it.

I jumped on this thread as i was having similar issues as Tenn_CB400F with my 400F.

I did the testing as suggested in this thread and determined  the voltage loss was in the ignition switch.I ordered a kit from CMS knowing it had mixed reviews. I was excited to have 1 key for the seat and switch.

Also found an NOS fuse block.

Before replacement  Static  Battery 12.52v headlight and most everything 9.6v
After replacement    Static  Battery 15.48   headlight and most everything 9.9v

Then i put the NOS fuse block on and voltage dropped to 9.4v. put original fuse block back on.

This is the perplexing part...
I just bought this bike last October . finished the restoration a month ago. I noticed at some point that putting the key in the "P" setting everything would work as normal. all my other bikes just the tail lamp comes on and you can remove the key.
This new switch behaves the same way and you can ride with the switch on "P".The only exception is that everything including headlight has 11.6
volts and everything brightened up.I did not check voltages before swap
Looking at the wiring diagram to see if some of the wires in the plug going to the switch are in the wrong position. they all look good.

[Ozzybud]

Upon looking further it might have the wires in the wrong positions going to the switch.

Its really unclear in the wiring diagram as the which colors go where?

does anyone have a clear diagram as the where the 5 colors go?

 it looks as if my red is in the center position. all the pictures of wiring harnesses have it on the end.

[bryanj]

If everything works in the P position the wiring is wrong
Is it a replacement harness or original?
Did you remove any wires from ignition block?