Author Topic: No power to the fuse box except the 15A, What's going on?...almost have it updat (Read 6370 times)

nhodges · « **on:** February 13, 2011, 12:54:18 PM »

Good Afternoon,

I am currently wrestling with the electrical demons on my '74 CB750K. The issue I am having is that at the fuse box I am only getting power to the 15A fuse connection. Turn the key and the only thing that works is the back brake light (is that right I thought the 15A was the main, and one of the lesser fuses operated the tail brake light) I tried trouble shooting on the forum and haven't found any fix yet; here's what i have done:

-first things first, got a wiring diagram
-battery is new and fully charged
-all new fuse (5A,7A,15A)
-cleaned the fuse blades to a bright shine, tight connection
-opened the harness in the triangle and all the wires look good
-connected the black and red wire at the ignition and got power to only the 15A, so I believe the ignition is good
-don't know if it would matter, but i have a new starter relay on
-original points, no new ignition system, original coils (I jumped the old relay at the posts and the bike tried to turn over)

I disconnected the fuse box, turned the key, and with a multi-meter check the power coming to the fuse box at the female connects and the only one getting power from the battery is the red (15A) feed. Really getting tired of tearing apart the triangle, anyone know whats up. I really tried to search this before I asked, I hate making ppl have to repeat themselves. Hopefully its something stupid.

DarcyCB400F · « **Reply #1 on:** February 13, 2011, 01:34:22 PM »

I don't know if this applies but here goes anyway...

My '77 CB400F runs power to the headlight throught the starter button. What this means is that my broken starter button was to blame when I couldn't get power to both the headlight AND the headlight terminal in the fuse box.

I don't know if is helpful but thought I would throw it out there anyway.

DH · « **Reply #2 on:** February 13, 2011, 01:43:50 PM »

sounds kina like a malfunctioning key switch. You can jump the red
to black like you've done already, and then at the same time, jump (start by just touching) the remaining two wires (orange to brn/white)together, thus, bypassing the keyswitch. this action should fire up everything. Turn on the headlight. All fuses should be live at this point as well.
If everything works, the switch is bad. The 15 amp main is fed directly from the battery, and passes current directly to the keyswitch. If you jump (touch)only the red to orange at the keyswitch connector, only the park/tail should work........Make sure your grounds are all good as well. just a guess..May be something else. Does the engine even crank?
The main fuse is always hot
The headlight fuse is switched hot thru both key and headlight switches
The park/tail fuse is switched hot by keyswitch only when in position 2 OR when headlight is on.

nhodges · « **Reply #3 on:** February 14, 2011, 05:35:35 AM »

Hey thanks for the reply guys,

Didn't mention that I replaced the bars a little while ago, and since i had to run the switch wires through the new bars I figured it was a good time to clean all the bar controls and make sure they had continuity. So I don't think its a faulty starter button.

I have no clue electrically on this bike. So I guess my first question is related to power at the fuse box. With the key to the second position I thought I would have power running to all the fuses from the battery (is this right? or is it just too early and I am not thinking correctly). The engine does crank, I only know this bc I touched the two posts on the old starter relay with a wrench and it tried to turn over. Seems like this maybe the key switch, I thought it was good bc I am getting power to the 15A when I turn the key.

Silverback · « **Reply #4 on:** February 14, 2011, 06:57:59 AM »

As mentioned above, there is a switch on the right handlebar control that powers these fuses/circuits. Are your headlights turned on at the right handlebar switch? (Off/On lever)

nhodges · « **Reply #5 on:** February 14, 2011, 07:20:34 AM »

Hey SB,

Yeah I have the switch turned on, kill switch to run, key turned, and only have power to the main (15A), and the only thing lighting up is the tail brake. Won't be able to get back at it till Wed.

Keep the suggestions coming. Between suggestions and reading I hope to have a plan of action by then.

Thanx

Silverback · « **Reply #6 on:** February 14, 2011, 07:34:23 AM »

That tells me that the issue is in the ignition switch, or handlebar switch. I recently had a connection come un-soldered at the back of my ignition switch. This resulted in the same symptoms you have. Are you running 3-ohm coils? They can tax the power wiring and finish off any poorly soldered connections pretty quick.

nhodges · « **Reply #7 on:** February 14, 2011, 09:14:56 AM »

Now I'm thinking its the ingition switch too. the bar switchs should be good, I took them completely apart, cleaned, and repaired the connections. Also before and after I ran the wires through the handle bar I checked the right hand switch contols for continuity (everything checked out).

I'll monkey with it some more mid week and see what I can figure out.

Haven't really messed with the coils yet. As far as I know their the original ones that came with the bike. Once the power/switch issues are cleared up I am sure I'll be back asking questions about the coils (hopefully they work perfectly).

Bodi · « **Reply #8 on:** February 14, 2011, 09:59:02 AM »

the 15A main fuse should be before anything - unfused battery power goes to the fuse first, then fused power goes from the fuse up to the ignition switch on the red wire.
Everything else powers through the ignition switch. The lighting fuses get power from the black wire. There's a trick with the tail light, though, it may get power just from the main fuse when the ignition switch is in "park".
So: you should have power on the red wire all the time (with a good battery 15A and fuse). Switch to "on" and you should have power on any black wire, plus the lighting fuses. Switch to "P" and you should have a lit tail light but no power on the lighting fuses. Different years changed this parking light power a bit but later ones (I'm not sure about 74) all work this way I think.

Don R · « **Reply #9 on:** February 14, 2011, 10:05:55 PM »

If you changed bars recently take a look inside the headlight bucket, a connection may have come apart. download a color wiring diagram from the manuals that will help troubleshooting.

nhodges · « **Reply #10 on:** February 16, 2011, 03:11:16 PM »

Thanks for the help guys, here's an update

I worked on it all day and got power across all the fuses at the box. I had to repair the fuse box, put a new ignition on, and re-cleaned all the connections in the headlight (I used a round file this time); so now the tail light, head light, and indicator lights all work. I am really happy about this. But when I hit the starter button nothing happens. I checked the continuity on the starter button and it checks out. The starter relay is brand new and I don't know what else could be causing it to not at least try to turn over.

So bring on some more suggestions and bear with me, this electrical stuff is new to me

DH · « **Reply #11 on:** February 16, 2011, 08:54:56 PM »

Is the transmission in neutral when you push the start button?
A k4 is designed so that the starter motor will only operate when
the bike is in neutral, OR, if in gear, the clutch lever must be pulled
in. A clutch switch and starter motor safety unit work together as
a system/safety feature. Keeps the bike from lunging forward if the
driver hits the starter button with the bike in gear and the clutch out. Someone with more knowlege of the system will hopefully add
more as to how it works...

nhodges · « **Reply #12 on:** February 17, 2011, 05:57:22 AM »

Morning DH,

yeah the bikes in neutral. Not bc i knew that it had to be to start, but bc I have it on the center stand so when I need a break from the electrical I can clean the back wheel hub. Thanks for the input.

I am gonna get back at it, if no one comes in with advice I'll try the search function again, If that does produce an answer I'll start a new thread

thanx

Silverback · « **Reply #13 on:** February 17, 2011, 07:22:08 AM »

You said that you were getting continuity at the switch. Have you tested that you are getting continuity at the connector for the starter solenoid? ...or better yet continuity when you push the starter button (Meter yellow/red wire while grounding the other meter probe). The starter itself should be grounded to the case. You can potentially bypass the diode to see if it is the issue. However, if your neutral light is coming on it should be fine.

nhodges · « **Reply #14 on:** February 17, 2011, 02:34:49 PM »

Ok,

So here we go. after another day of messing with the electrical. I have the front turn signals, head light, neutral light, turn signal indicator light all working with the key in the second position. This was after I put the old starter relay and ignition back on (I bought the new relay and ignition from CB750supply, I don't really understand what the deal was with them) Also with the key in the second position the push button start works, theres not gas in the engine so its not going start....but it is at least trying. With the key in the final ignition position everything turns off and the push button start stops working

So now I need someone to explain what is causing this. I figured with the key turned to the ignition (final) position all electrical lights would turn off, but that the push button ignition would still work. (I am right or am I a huge idiot)

First time working with a bike and I started the electrical yesterday, so i feel like I've made good bit of progress. Just need a little more help and input

Thanks for all the support!

Silverback · « **Reply #15 on:** February 17, 2011, 02:36:40 PM »

Ok! I was looking at the wiring diagram that I posted and it did not have the right wiring for your bike, so I removed it. Sorry about that. I think that I am confusing things. The starter button, clutch and neutral switch all provide grounds for the starter relay. So, push the starter button, relay is grounded. Put it in neutral or pull clutch and relay is grounded. In order for the starter button to have an effect, the bike must be in neutral or have the clutch lever pulled.

Having said that check that these connections are doing their job.

Edit: I guess that I posted same time as you. Glad things are working good. Does final mean two clicks away from it's off position? If so, this is park mode and your tail light should come on. The first click is run mode.

mjstone · « **Reply #16 on:** February 17, 2011, 02:57:28 PM »

With the key in the "final position" you should have only a taillight lit. you should also be able to remove the key in this position. Honda did this so you could "park" your bike and leave a taillight lit so anyone coming up behind your bike in the dark could see it and maybe not run it over. I don't know anyone who uses this "feature". Most of us just use the first two positions, "OFF" and "ON". Hope this helps.

MJ

nhodges · « **Reply #17 on:** February 17, 2011, 03:23:44 PM »

Ok, Great!!

No worries SB, you've been a lot of help. That means everything is good to go. The only light not coming on is the oil pressure light on the panel, and I'll address that tomorrow. Now all I need to do is make sure I am getting fire to the plugs and I'll be ready to put some fuel in it and try and start her up.

Thanks for all the help. Feels good that have sorted through all that.

Spanner 1 · « **Reply #18 on:** February 17, 2011, 05:29:34 PM »

OP, I think your ignition switch is TURNED 180 deg. from it's stock position, hence ign. is 'on' in the #2 position and 'goes off in the last position'.... seewhatimsaying?

Edit !..... scratch that

.... actually wouldn't make any difference to the key position, oh well

News:

Author Topic: No power to the fuse box except the 15A, What's going on?...almost have it updat (Read 6370 times)

DH

DH