Topic: CB400F shut off while riding and now has no electrical power!!! Need help!!

[inv3ctiv3]

So I changed the oil today and cleaned up the wiring a little behind the headlight (the PO had them just kind of hanging out) and went for a nice little ride in the hills and the bike was running tip top until it just all of a sudden lost all power and shut off. I thought it was out of gas so I quickly switched it to reserve and bump started it as I was still rolling and it fired up and just immediately died again. I couldn't bump start it and it has NO power to the headlights or anything. I'm completely stumped, I thought maybe the ignition switch went out or something? I'm gonna spend all day tomorrow trouble shooting it but I wanted to get your guys advice first, any idea on what to test or look for? I'm thinking rectifier or ignition switch?
Thanks!

PS it's a 1975 CB400F with 25k miles.

[LesterPiglet]

Why not check the fuses first? Then go back inside the headlight and check everything is still connected.

[inv3ctiv3]

Why not check the fuses first? Then go back inside the headlight and check everything is still connected.

I did both those things, I didn't actually unplug anything behind the headlight either I simply just re-organized them.

[LesterPiglet]

Don't take anything for granted. Unplug each connection and plug it in again. Also if you have a spare main fuse replace it, sometimes these blow at the ends where you can't see the filament.

[bjbuchanan]

Check your points connections, or the wires to the coils. I have had times where I could bumpstart it and it would die right off that the bullets where "connected" but not really, they just came apart and wouldn't really grab

[Fritz]

If power cuts out completely, always start with the power source: With the ignition off, measure the voltage across the battery terminals. If it's below 12V, charge it. If it cannot hold charge, replace it. Also, you should check that the ground connection between the battery and the frame is good. I don't know the CB400, but there should be a ground connection between the wire harness and the frame too. Check that for good electrical contact. Measure resistance between the frame and the battery negative terminal and between any green wire and the battery. It should be well below 1-2Ohms.

Next the fuses: They can _look_ fine, but you should test them with the meter for continuity.
The battery holder can go bad:

Then go on with the ignition switch: Measure voltage between the red wire and ground/frame. If you don't see 12-13V, re-check your ground connections, the positive connection of the battery to the solenoid/wire harness and the fuses.

Then measure between the black wire at the ignition switch and ground with the key in the 'on' position. No voltage means that your ingition switch might be toast.

Only after the last checks fine, it's worth spending time to check all other connections.

Cheers
Carsten

[inv3ctiv3]

So it did end up being the main fuse....It looked fine but the end was broken off on one side and you couldn't tell by taking it off and looking at it, only testing it proved it to be bad.  BUT upon further inspection it looked as if the fusebox had melted at one point and the PO did a shotty job of fixing it so my friend and I just built a new fuse "box" with updated clip fuses instead of the old glass tube ones:

[oldbob]

BUT upon further inspection it looked as if the fusebox had melted at one poin

That's pretty common. The contacts that hold the fuses get oxidized over the years, and then act like the heating elements in a toaster.

When I first put my 400 on the road for testing, everything electrical was good (the float valves were a different story). The next morning, the electrical system was completely dead. Melted fuse box. I got lucky that it didn't happen while I was far from home.

I ended up getting a new fuse panel from HondaMan. I also cleaned *every* connection in the wiring harness. You might want to look at the three wires that come off of the alternator. Mine were fried.

Bob

[inv3ctiv3]

BUT upon further inspection it looked as if the fusebox had melted at one poin

That's pretty common. The contacts that hold the fuses get oxidized over the years, and then act like the heating elements in a toaster.

When I first put my 400 on the road for testing, everything electrical was good (the float valves were a different story). The next morning, the electrical system was completely dead. Melted fuse box. I got lucky that it didn't happen while I was far from home.

I ended up getting a new fuse panel from HondaMan. I also cleaned *every* connection in the wiring harness. You might want to look at the three wires that come off of the alternator. Mine were fried.

Bob

Yea I plan on cleaning all the connections as well, I noticed the connector from the battery rectifier is toast so I may order a new rectifier from 4into1