Topic: 1971 CB500: Melted wires behind headlight

[jeff d]

I was investigating why the tachometer light had no voltage, and found this surprising mess.

It appears that something got really hot in there.  It's possible that some shorting occurred, but really the damage looks more like heat damage.  The bike's fuse appears old and is not blown, and everything other than the tach bulb had been working!

Does extended headlight use do this? Or is there a missing heat shield of some kind that should be protecting the wires from the headlight?

Everything is super stock on this one-owner bike.  There are no add-on wires or accessories (other than a piece of electrical tape someone used to prevent the melted wires from touching).

CB500 wire melt 1 by Jephtha Studios2, on Flickr

Instrument Wire Melt 2 by Jephtha Studios2, on Flickr

Instrument Wire Melt 3 by Jephtha Studios2, on Flickr

[Bankerdanny]

What kind and wattage headlight bulb do you have? If you are running a high output halogen bulb that could have caused the wiring to overheat.

[jeff d]

What kind and wattage headlight bulb do you have? If you are running a high output halogen bulb that could have caused the wiring to overheat.

Stock headlight.

[bryanj]

It shouldnt get that hot but a corroded/bad therefore high resostance connection might

[Bankerdanny]

Then something was wired very incorrectly. Head over to vintage connections and get the K1 or K1A kit and replace the ends on all the damaged wires. http://www.vintageconnections.com/Products/Kits

[RickThomas]

Certainly not normal, especially with the stock bulb. Probably a short due to exposed/chaffed wiring. Unfortunately, the name electrical tape encourages amateur mechanics to use it as a cure all for electrical problems.

[RAFster122s]

Vintage Connections has terminals, wire, and crimper for effecting your repairs in a professional manner. Recommend you replace the damaged wiring and solder joints you splice your repaired section. One option would be to open the harness to replace the entire run of that wire with new but that would require new sleeving and quite a bit of disassembly. Use a good quality heat shrink on your repairs if soldering your splices. A good quality heat shrink will have an adhesive inside the tubing which helps make the repair watertight, helping to lessen chances of wire corrosion because of moisture.

[PeWe]

Bad grounding? It look like the ground is weak, overloading the thin green wires.
This has been up before in other threads.

Make sure that the thick ground wire from battery (-) is properly connected to frame and engine. Paint is grinded off where connected. Frame both sides and engine case.
Green ground direct to frame OK too.

[jeff d]

Thanks everyone. I was not aware of vintageconnections, those OEM style connectors are what I need. 
The two wires melted through the black sleeve are the tach and speedo light harnesses. I’ll try to find some intact original versions of those on eBay rather than splicing in the middle.

Interestingly, the bike tach and speedo only have a single bulb illuminating them. The schematic in the manual for cb500 k0 for the US version has 2 bulbs each for tach and speedo. Perhaps this bike was originally sold overseas and imported.

The bike is super original as Mr. Honda intended, and I’m trying to keep it that way!

[bryanj]

The early 500 only had 1 bulb rach, small clocks, chrome back plates with a big hole, straight cable inlets and a different angle on the mounting plate.

Anything else?

[jeff d]

Bryanj, that is great info.  This is probably an early model then. 

Where can I find more info like this?  Thank you!

[bryanj]

Parts books mate

[Don R]

Be aware the vintage Honda connectors you need are the smaller size.  I've gotten the bigger ones a couple times by mistake.