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Discussion Starter #1
Hello everyone, Western NY here, cold & wet most of the time, so barn find bikes abound! I found a cute '79 Honda CM400 for my daughter. Budget constraints meant that I could only afford a fixer-uper. It's a '79 CM400 with 11K on the spedo. It was missing the seat, tail lights and rear signals, so I replaced those things with aftermarket. After a lot of other work, (leaky carbs, petcock, etc...) I got the bike to fire up. The left hand turn signals function fine but when I turn the switch to the right it causes the flasher unit to buzz like an angry bumble bee. The RH signal lights do not flash. I have checked the bulbs, switching them from right to left and it still acts the same way. I am inexperienced with electrical issues and really need some help to get this ready for my daughter's upcomming birthday. Any help or advice is appreciated!
 

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Discussion Starter #3
Yes, I swapped out both bulbs and they work on the left side. Perhaps the switch itself needs to be checked out for a bad wire?
 

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I'd try taking that switch apart just to investigate.. It's pretty easy to get apart, and once you're in there it's a simple design. After you figure it out, it won't hurt to lay some dielectric grease in there, and I wouldn't be shy about using plenty.

GB :mrgreen:
 

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Discussion Starter #5
I'll try pulling that switch apart tomorrow evening and see if I can find any obvious problems. So what is dielectric grease and what does it do?
 

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MichaelP309 said:
I'll try pulling that switch apart tomorrow evening and see if I can find any obvious problems. So what is dielectric grease and what does it do?
Dielectric grease is an insulator, generally silicone based. It's good for lamp bases on trucks and trailers (as Ford applied it in the 80s) to slow corrosion. When used for ignition connections it slows corrosion and fills gaps between solid dielectrics so there's no air gaps. Since air has a much lower dielectric constant than solids, minute air gaps with high voltage applied makes the air gaps arc first leading to heating damage to the adjacent solid dielectrics.

Here is a good YouTube video that pretty much 'splains it all. It's good stuff and restorers like us should consider using it on all those bullet connectors, especially on connectors associated with the charging system or higher currents.

 

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You have a dead short to ground in the right side wiring to the signals.... could be anywhere from the switch to bad sockets in a signal unit..... If memory serves, you should be able to test if the switch is good simply by unplugging both light blue wires (in the headlight shell) from the light blue wire coming down from the switch.... If it still "buzzes", the switch or that one wire coming from it is shorted, if not, it's from where the other two light blue wires were plugged in to/and possibly including one of the signals.....
 

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I was thinking he had a short somewhere Steve, but I kinda thought he'd be popping fuses or melthing something?

GB :mrgreen:
 

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Nope...the flasher module uses enough current that the fuse generally doesn't blow until the bimetallic strip inside the flasher heats enough from rapid, repeated cycling (buzzing) that it fuses closed (welds itself)...THEN the fuse blows....
Since the left side works, the wiring is fine at least TO the switch.... The short can be anywhere from there onwards to where the flasher bulbs are.... A shorted socket would cause this problem, but so would a shorted wire leading towards it....Could even be as simple as one of the light blue wires accidently plugged into a green wire....
He'll just have to unplug one part at a time until it doesn't "buzz" when activated......
 

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Discussion Starter #11
You guys are very helpful, I'll get on this tonight after work. Thanks for sharing your knowlege and info. I'll refer back to your messages before I start!
 

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You can take the bulb out of the socket (theoretically opening that end of the circuit) and start from the turn signal switch (switch off) using a test light with the clip connected to the battery hot post. The light should not go on. If it does, look for any wires that have been pinched between metal parts, look at places where the wire passes through any holes in a metal part, and if you haven't found the short yet try disconnecting the socket lead from the light blue wire and test the socket. At any point that the "hot" test light goes on, you're reading a shorted wire. With the bulb out and the turn signal switch off, you've isolated that circuit. Anywhere that the wire is compromised, I find I can use a product called "Liquid electrical Tape" to coat the spot and then wrap it with electrical tape. In reality, I have a rather bad habit of simply leaving the whole thing alone, disconnecting both ends of the offending wire and running another wire in its place, maybe by a safer route. I sometimes just leave the offending one there to confuse me in the future.
 

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Discussion Starter #13
Okay, I should be able to find and figure out a short. This is much better news than someone telling me that I had to replace the wiring harness or some such Herculean feat of electronics that is simply beyond my capabilities. It's been raining here all day, my arthritis is killin' me so this task is now on hold till it's warm and dry outside. Besides, water + electricity = bad things.
You guys have been a great help, I can't thank you enough!
Soon I'll be looking for help with a barn find 78 CB750 for my son! But that's a whole different forum...
 

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OOHH OOOOH, I gotta see this 78 750 find!! That was my first street bike. I still miss her. Everyone here gets the pleasure of hearing that everytime someone mentions a 750.. :roll: Those SOHC bikes are trench diggers on hot pavement!

GB :mrgreen:
 

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Discussion Starter #15
Thanks for all the help guys! GB, my 750 project was purchased for $600. It's a '78 CB750K with a whopping 13,627 miles on it. When I am able to get it out of the garage and place the tank and seat back on it, I'll take a pic and post it. It's a barn find also, but I didn't know that mice had made the airbox and carbs their home. After cleaning off 15 yrs of crud, (yes, it's been parked since 1994), I realized the stink was comming from the airbox. Dead mice, yech! Carbs were toast, no bring them back to life. Scored a set off ebay though and when the 400 is done for my daughter I'll start the 750 project!
 

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Discussion Starter #16
Okay, this is the best I can do cause it's still raining out. The above pic is my daughter's low budget bobber project. I got the bike with 10,000 miles on it and I paid $350. I fixed it up to the best of my limited abilities. It's a testiment to the quality of these old bikes that when I finally got the carbs to stop puking gas all over the floor that it started with a little press of the button and the engine just purrs!
I hope that I have as much luck when I replace the carbs on my 750! Wish me luck with that one. I'd like to give it a low budget cafe makeover. With it's 4 into 2 pipes that should look good!
 

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That's a pretty good lookin bobber man. Kudos to you.

Your 750 has the exact same pipes as mine did! Man I'm gonna envy you seeing this one come together... You lucky bastige!! :lol:

GB :mrgreen:
 

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Discussion Starter #18
Many thanks to those who replied to my issue. I opened up the headlight and found that the hot wire for the signal was plugged into a ground! A little educated guessing on my part (you guys on the forum educated me!) and it's working properly again! Obviously the previous owner was an even bigger electrical dummy than me!
Thanks again!
 
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