Topic: K6 electric issue

[11braujm]

Hello! I'm new to the forum and this is my first post. Here's the back story. Last week I was doing some barn work and while walking around, I found this 1976 CB750 sitting around the back of the barn. I asked the owner about it and he said I could have it for $100. Paid the man, got the title. He kick started it, rode it around to show it ran, and I brought it home. When I got it home, the lights would come on and the horn worked, but the battery didn't have enough cranking amps. I went to start it later and there was no power at all. No lights or anything. Had the battery tested and found it was bad so I bought a new battery. There's still no power and its not getting a spark. Checked the fuses and they look good. Anything major I should check? Thanks for the help. Here's a picture of my find before purchase.

[goldarrow]

Great score on the bike And welcome!

Fuse may look good but could be bad. Check fuse again with meter

[greenjeans]

I'll give you $200 for it as is 

Check the fuses.  If you saw it run and drive, there's not much else that would cause everything to fail.

Make sure the new battery is hooked up correctly - that would do it.

[ekpent]

Is the key located up by the handlebars ? if so they can pull the connector apart sometime under the gas tank.

[11braujm]

Thanks everyone for the input! The key is up by the handlebars. I pulled the tank off and looked at the connector. The rubber boot was full of water and one pin was broken off. Cut off the connector and ordered a replacement. Twisted the wires together without the connector and still got nothing. Checked the fuses and they are good. All other connectors look good. Battery is hooked up right.

[bjbuchanan]

Absolute no power can only mean a couple spots really. Tight connections at the battery posts and the Red connected off the battery. The red will tee off battery/starter solenoid wire and go to fusebox 15A. Then out to keyswitch where it is 'crossed' to the black,brown/red and brown which return go to fusebox.

Pull those fuses and shake around, swap them out. Bulb fuses are notorious for looking good but being bad. With how neglected that bike has been you gotta check the back of the fusebox too. Look for the connectors at the fusebox contacts to not be good. Resistance gets them hot and they melt out of the fusebox. Or the fuse filament gets warm and separates from the fuse ends

[11braujm]

Alrighty I changed all of the fuses just to be safe. I pulled off the ignition switch and found this.

I think it arced and helped lead to some corrosion. Unfortunately, I'm working up in the mountains right now so my only tools are what came with the motorcycle. I'll remove the fuse holder when I get a smaller wrench. It does like part of it is melted. I'll resolder the ignition and test it as well. Below a picture of the connector I found.

[bjbuchanan]

Looks like you got yourself some 'improvements' to deal with. Not the end of the world, just gonna take some work.

Get yourself to Harbor freight and buy the cotter pin set they have for 6$. It is like 200 piece set. Use the larger cotter pins to de-pin all of your connectors and clean then up using scotch-brite. I don't like sandpaper because it removes material compared to just cleaning them.

The large cotter pin will need a little filing but it makes an excellent de-pinning tool for dirt cheap. After that you have cotter pins for a lifetime too lol

[11braujm]

Finally back home and with internet. I removed the headlight and started trying to organize the mess. Unfortunately, the PO had done some work behind there too and my wiring diagram has a few different colors so I'm trying to sort through that. I've taken calj737's advice and started cleaning the connectors. I've had to replace a few.

A new key switch and fuse holder are on the way. The old key switch was corroded on the inside. Fuse holder was melted but still worked as I found out today. I ran the wires together for the ignition and immediately blew the 15A main.

I'll have to make my way to harbor freight to get those cotter pins. How easy is depinning those connectors?

[Spanner 1]

Nice find for $100... !! Please don't put bigger than a 15A fuse as a Main fuse as meltdown can result ! If you connected Red to Black @ the ign. switch and the main fuse blew immediately ( considering the bike already ran ), then it looks like a dead short somewhere on the Black wiring. Remember on Honda bikes Black is + 12V when key is turned 'on'.... ( not ground , which is Green wires ).....

[bjbuchanan]

http://forums.sohc4.net/index.php?topic=78308.0
http://forums.sohc4.net/index.php?topic=7606.0
oldmanhonda.com

Those are useful links. I like oldman honda because you can turn circuits on and off to trace stuff. The color coding for SOHC4's is all the same, just varying equipment. Inspect your starter button and see if it is broken. The starter button is a known problem on k6 models due to the combined headlight switch that is always drawing current through it. If it is broken it will blow a fuse as soon as you connect black to red. One of the hidden problems

Black is switched 12v
Green is ground
Brown is lighting
Brown/red is headlight
***Black/red out of starter switch is power to headlight on k6, one key difference compared to older models where headlight could be turned off

[11braujm]

New fuse holder and key switch. Its no longer blowing fuses but still not getting power. I found my multimeter but remembered it quit working a few months back while working on the tractor. More news to come.