Austin Cafe Racer

Replacing the Kill Switch and Starter Button

This first post is more exploratory than practical. I wanted to get my bearings and take a peek inside to understand what I was dealing with in terms of wiring. Once again I was amazed at the complexity of the industrial engineering concerning the button and switch fabrication. Of course, we can make this entire system simpler and more pragmatic which is what I intend to do in the next weeks. First things first let’s take the thing apart.

The housing is too bulky and it certainly doesn’t fit in with my new master cylinder. I’m currently looking for a sleeker aluminum alternative.

It’s no surprise its pretty dirty in there.

Black electrical tape.. tisk, tisk, the previous owner must have been in here sometime ago.

Bottom enclosure with button removed.

Starter button, all taped up and nasty.

Here you can see some type of green stuff growing on the exposed wiring.

Bottom of the starter button. Metal plate is rusted and dirty.

Metal plate removed.

These pieces represent the entire starter button disassembled. I’m consistently surprised by how tiny these little components are. Seems a bit overkill for a switch. I can’t believe they didn’t have anything resembling today’s mini SPDT or DPST switches.

This shot is of the wiring connected to the three metal leads that the button slides against. Like many old Honda CB owners, I experienced the occasional starter button sticking problem. The frayed ends of the yellow/red wire explains the occasional main fuse blowing. If the black wire is grounded in any way the main is going to blow.

Here is the bottom of the wiring assembly. We can certainly do better than this right? The strategy is simple enough. This is a three wire setup, where the black wire is feeding power, the black/red wire is the power to the headlight, and the yellow/red wire heads to the starter. So, the starter button is actually doing two jobs at once, almost like a simple relay circuit. First, the button in it’s up or open position is closing the circuit between the black and black/red wires, feeding power to the headlight. Second, when the button is pressed in the mechanism slides the tiny copper leads to connect the black wire to the yellow/red. This process turns off the headlight, while the starter turns the engine. When you let go of the button it reconnects the black to the black/red. BRILLIANT! But old fashioned.

So we have two choices here:

1.) We can go the simple Brit style way and connect an on/off SPST button that closes the circuit between the black and yellow/red wires. This process eliminates the black/red wire (headlight), which means we have to rig another simple on/off SPST switch somewhere to turn on the headlight. This is kinda cool, because we can have control of the headlight bulb, turning it off and on when we please.

2.) Or we can replace this overcomplicated starter button mechanism with a mini SPDT switch that will do the same job. This presents two problems:

a. We need to find a mini switch that will fit inside the bars. This means finding a switch whose body along with soldered wires is shorter than 7/8inch.

b. If we choose not to mount inside the bars, we can find any size button and relocate it somewhere else (easy). What makes this problematic is being unable to push the button while turning the throttle while simultaneously holding in the clutch in.

These are issues I’ll be pondering in the next few weeks.

The kill switch, on the other hand, is a more manageable system.

This is a simple two-wire setup. Our original switch was three way, with an off-on-off routine. In reality this is just a single throw switch.

This tiny little clip is the first thing you have to remove to pop the red switch out.

Careful not to lose these itty bitty pieces.

Here are the two leads, black and black/white. The red switch has a metal tab that closes the circuit when it falls between the two round leads.

Check it out. Another small ball bearing. Those 70′s era engineers were clever but also kinda weird. The ball bearing was used to give the switch that tactile feel of “clicking” when you turned it.

Here you can see the worn grooves where the ball bearing had rolled over for the last 35 years. Once again, we can make this switch much more aesthetically pleasing as well as relocate it somewhere else on the bike. The wiring is a piece of cake, we just need a simple SPST switch and solder the two wires to each lug. It will be the placement of the switch that will be difficult, not the actual placement but the design. It has to look good, not out of place.

I’ll post more on my progress in the next few days. Remember.
Don’t be afraid to take things apart.
Have fun.