Topic: Front Brake Light retrofit of 78K frame to 78F front end

[scubanerdnick]

Hi everyone.  New to the forum (military guy stationed in VA) and I did my best to see if there was another thread on this topic but couldn't find one.  The front end of my newly purchased K8 is a Super Sport model from the same year (I think).  Because of this the front wheel has two disc brakes (sweet) which seem to work well mechanically.  However, I could not figure out why the brake lights on the front don't operate.  I attempted to follow some good threads here and engaged the front brake hard to make sure the issue wasn't there before I took off the headlight and saw the mess of wires in there. 

Initially I was pretty stoked because it looked like a green/yellow wire in there was disconnected so I popped it back in and nothing.  I then traced it back to origin and found coming off the front brake there is a green/yellow and a black wire.  I looked at the wiring diagram and attempted to follow along (moderately successful) and plugged the green/yellow wire into the corresponding green/yellow and then the black wire into an open black connector.  After doing this the brake light is on constantly and no engagement of the front brake or rear brake changes things. 

I then proceeded to disconnect each wire and found that the black wire (power I'm assuming) causes the constant brake light.  I went so far as to swap the wires to see if maybe the person who owned before me had done something to them and same issue persists, whenever black wire is plugged in brake light is on constantly.  So my question is would there be any wiring loom differences between a '78 K and a '78 F which would make the brakes do this OR is there an incredibly simple solution I am missing?  (Addendum: I just looked and the wiring harnesses for the 78F and 78K are different)

That being said is there a workaround to get the brake lights to engage that anyone knows of? 

Attached are a few pictures of the brakes and the wires I'm talking about. 

[scottly]

The switch for the brake light should be in the master cylinder on both the K8 and the 77/78F master cylinders, while all the other 750s used a hydraulic switch mounted on the brake line splitter on the lower triple tree. Which master are you using?
BTW, someone has upgraded the calipers to the '82 and up two piston calipers.

[scubanerdnick]

I had not considered the calipers might be different too.  Is it possible the front end is NOT in fact a 78F?  I just assumed when I bought it because that's what the guy said it was but now I'm maybe not sure. 

Anyway the master cylinder looks like a aftermarket one.  It could be original but looks pretty new-ish.  Attached are some pictures of it.

I really appreciate the help. 

[scottly]

Are the black and yellow/green wires in the last pic coming out of the MC?

[robvangulik]

I can't see a switch anywhere....I think the previous owner (PO) fitted a (better?) master and just omitted the front brakeswitch!

[denward17]

Here's a pic of the '78 K underside of master with toggle switch..

I pulled in the brake lever so you could see the toggle switch.

[scubanerdnick]

Scottly - yes the wires are coming directly from the master cylinder.  I tried to show that in the photos but need to brush up on my photography skills.

robvangulik - Where would the switch be?  Maybe its something I didn't focus on in the pictures.  I'm new to almost all of this so I really appreciate everyone's help.

[scottly]

OK, that's the wires from the switch. With your ohm meter connected to the two wires, there should be no continuity until the brake lever is pulled. The switch is plugged into the MC from the back, and has a small plunger that the lever depresses when the lever is released. When the lever is pulled, it allows the plunger to extend, turning on the light. If the switch has moved back out of position, or the plunger has broken off, the switch will always be on.

[BenelliSEI]

Two wires coming from the master? They should close the circuit when you pull the lever. Now you need to connect them to a power looks, that feeds your brake light…

[BenelliSEI]

OK, that's the wires from the switch. With your ohm meter connected to the two wires, there should be no continuity until the brake lever is pulled. The switch is plugged into the MC from the back, and has a small plunger that the lever depresses when the lever is released. When the lever is pulled, it allows the plunger to extend, turning on the light. If the switch has moved back out of position, or the plunger has broken off, the switch will always be on.

Scott posted as I was answering and his answer is more complete!

[scubanerdnick]

I took some more pictures and maybe they will better illustrate what I have here.  I just want to confirm the wires inside the headlight should connect to matching wires (IE: green/yellow connects to green/yellow and black to black).  The stop switch (I think?) is pictured in the first picture (poorly), the other images might help better illustrate what I'm doing.

Its hard to make out but its a square button that can be depressed and returns after depressing.  It is tactile in response but doesn't appear to touch any part of the brake lever as was the case in the photo denward shared.

I do not have a ohm meter but I will go get one and test it.  Never know what you need until you don't have it...

[scottly]

Yes, the wire colors match.

[scubanerdnick]

Okay so with all of your help I think I diagnosed it.  The stop switch when depressed does turn off the brake light meaning it should function if the brake lever was depressing the button properly.  I think my issue is that no portion of the brake lever touches that switch and closes the circuit.

Here's another picture of the small button in relation to my brake lever and after I tested it it worked just like you guys indicated it would.  So looks like I need to get a new lever until I get the K8 front end ready to go.

Thanks everyone that took the time to help out a new guy with this.  I was so focused on the rats nest of wires I never even thought to look at the master cylinder for a switch until you guys mentioned it. 

[scottly]

Is that a nut under the brake lever??? One possible fix for the switch would be to fit a banjo bolt with an integral switch.
BTW, I would keep the later front end, especially since it has the superior two piston caliper upgrade! You can use the K8 spoked wheel if you fit thinned 550 brake rotors as described in this thread towards the end:
http://forums.sohc4.net/index.php/topic,89771.0.html

[scubanerdnick]

I just read through that and its really interesting.  You guys are wizards with some of this stuff.  I have a long way to go.  I hadn't planned on keeping it but I will probably do so now.  The increased braking might be worth looking into.  I don't like the LOOK of the comstar wheel on the front but the brakes work fantastically.

So after troubleshooting the brake light all day (ugh) I now can't seem to make the turn signals function anymore.  I decided to stop for the day and start drinking so I don't get discouraged.  On a related note the wiring nest that gets rammed into the headlight is straight up not a good time.  I like to work on computers and can't help but wonder why these wires are so damn long everywhere.  The cable (wire) management inside the headlight is just awful. 

Any tips on dealing with the long wires and those small bullet style connectors?  I went from having working turn signals but no front brake light, to now not having turn signals but diagnosing why I have no front brake light.  I think I finally understand why owning these old Honda's is for enthusiasts and not novices.  It's Miller time.

[Don R]

  I spent a couple hours fixing my K1's turn indicator light today. I enjoy the discovery part and the fixing part is rewarding in its own way when you ride. I had wired it incorrectly when I added turn signals back to the bike. I mistook faded green for light blue.

[70CB750]

I just read through that and its really interesting.  You guys are wizards with some of this stuff.  I have a long way to go.  I hadn't planned on keeping it but I will probably do so now.  The increased braking might be worth looking into.  I don't like the LOOK of the comstar wheel on the front but the brakes work fantastically.

So after troubleshooting the brake light all day (ugh) I now can't seem to make the turn signals function anymore.  I decided to stop for the day and start drinking so I don't get discouraged.  On a related note the wiring nest that gets rammed into the headlight is straight up not a good time.  I like to work on computers and can't help but wonder why these wires are so damn long everywhere.  The cable (wire) management inside the headlight is just awful. 

Any tips on dealing with the long wires and those small bullet style connectors?  I went from having working turn signals but no front brake light, to now not having turn signals but diagnosing why I have no front brake light.  I think I finally understand why owning these old Honda's is for enthusiasts and not novices.  It's Miller time.

My Red bike is K3 with 78F engine and wheels and fork.  Compared to the K0 brakes - even with a dual disc conversion - 78F brakes are great.  Comstars - I kinda like them; matched them on th sidecar and I also run tubeless tires, major plus in my book. 

For wiring, you can get connectors here:

http://www.vintageconnections.com/Products/Connectors

They even sell crimping pliers but I got mine from alibaba or some other cheap chinese place.  It takes little practice but you will be able to repair or update your harness correctly.  If you ever made Cat5 or Cat3 cable, wiring motorcycle is easier than that.