Charging System, Wiring, Lighting
6 posts • Page 1 of 1
I keep blowing fuses when I press the horn button. Replaced the switch and still having the problem. Have a short somewhere. Took the horn off and adjusted it and now as soon as I turn the key on the horn goes off. If I press the horn button it blows the fuse. Anyone have this same problem?
1965 Honda CB77 Super Hawk
This sounds like you may have a short circuit to ground caused by a worn wire. The rough edges around the wiring holes in some handlebars can be hard on the insulation and expose the copper inside. The holes in the headlight shell can do this too.
I would suggest that you inspect very carefully the wires coming from the horn. It's unlikely that there's a break inside the wiring harness but if there were one it would be unlikely to short to ground. I think that the horn is always connected to the positive side of the battery. The button works by grounding the wire and thereby completing the circuit.
I can't say any more that might be helpful. If you don't have a multimeter I suggest you buy one; even the cheap ones are pretty good these days. Then start inspecting and checking.
Here's a link to a CB72/77 wiring diagram.
Tim lays out a good troubleshooting strategy.
The symptoms suggest the ignition-switched-hot Horn wire has grounded somewhere to the frame, bars, headlight bucket or horn assembly. Depending on year/model CB77, the horn wire color is either Light Green or Black. Another possibility is that wires are cross connecting or grounding inside of the left-hand Horn & Dimmer switch assembly itself.
I don't see a Classified section in this forum, or this would be placed in the classified section: We offer a Honda handlebar switch reconditioning service found in eBay: https://www.ebay.com/itm/115808278042.
1967 CL77 305 Scrambler
I have a 1965 CB77E. The horn switch has one black wire. The horn tested good. Does both black wires that plug into the horn hot (12V)? I found that only one black wire has 12volts. Is that correct?
1965 Honda CB77 Super Hawk
That should not be. Both sides of the horn need to be 'hot'. Otherwise, no current would flow through the switch when you push it and the horn wouldn't work.
I rebuilt my CB77 horn a few months ago and I think you may have found the cause of your problem. On mine, the two wires enter the horn through a grey rubber rectangular seal that is probably in poor condition. You can pop the cover off of the horn with a small screwdriver and have a look at what's happening inside. There must be a short to ground in the horn somewhere, perhaps at the seal or perhaps inside. That would explain why the horn is always on when the key is. As for the fuse blowing, the switch-side wire must be connected to the 'hot' side somehow. This would blow fuses if the current is flowing to ground but not flowing through the coil in the horn. Normally the horn provides enough resistance to prevent blowing the fuse.
So, the hot wire should be connected to one side of the horn coil and nothing else. The button wire should be connected to the other side of the coil and nothing else until you press the button. Both sides should always be at 12V. The horn coil should have no direct connection to ground, except through the button switch of course.
I hope this is helpful. If you still have problems it might be useful to post a photograph or two.