Tuesday, 28 April 2020

QR50 - Wiring

It's a bit early to be looking at wiring up the QR50, but since we are on lockdown and my workshop is a few streets away I have resorted to bringing stuff to the house to work on. It's good to bring the wiring indoors - it's a nice clean job that you can do at your desk in the study.

This is virtually all I have, apart from the toasted generator stator I showed you in another post. This is the CDI unit:


And here it is again with all that insulating tape removed. If you look closely, you will see that some of the wires have been cut very short:


This is the whole 'harness', minus the sleeving. There isn't much to wire up on a QR50, but it is not supposed to look like this:


Before we start though we need a circuit diagram. Through a lot of research, Honda parts lists, generic CDI system diagrams and looking at the charred remains of the original loom I have come up with this:


There's a lot going on in this diagram, besides the connectivity of the various parts. Let's look at the way the system functions:

  • The Black and White wire (BW) wire is the exciter - it provides AC voltage to the CDI module
  • The Blue and Yellow wire (UY) is the trigger - it uses the hall effect sensor in the rotor to tell the CDI unit when to fire the coil
  • The kill switch earths the exciter coil through a second BW wire, preventing the ignition from working.
  • The Green and Yellow wire (GY) is connected to a micro-switch in the rear brake lever. According to the user manual, the engine won't start if the brake is not applied, and there is a spring loaded lever to hold the brake applied while you start (this disengages as soon as you squeeze the brake). I assume (at this point) that the switch is intended to break a ground connection when you apply the brake, but that this has no effect when the engine is running...
  • The Black and Yellow wire (BY) is the wire to switch the ignition coil.
  • The Green wires (G) are grounds.
In addition to the functionality, I have used this diagram to indicate cut wires - each cut wire has a number (1 to 16), and each cut wire has a connector (male, female or double female). The harness layout is shown in a simple sketch with rough dimensions; I have shown a length against each cut wire and summarised these to determine the total length of each colour. This list, along with the list of connectors, tells me what to order. I have followed Honda's practice of using the same 1.0 mm² wire throughout.

I'm going to use original type Japanese 3.2 mm bullet connectors throughout. These work beautifully and are protected from the weather - but you must select them according to the wire diameter.



Here are most of the parts we need:


First, I am using some tube crimps and solder to extend all the wires from the CDI unit to match the only remaining original wire, the ignition trigger. This is often tricky, as 40 year old wires are often too dirty to solder; this one has been OK, probably thanks to all the insulating tape.


I've protected these joints with heat shrink sleeving. I bought a selection of 8" lengths in various colours from eBay, and very useful it is too.


This is the CDI unit, finished with sleeving and boots as the original was. That large boot with the section change was made from a short length of heat shrink sleeving, partially shrunk over a small bottle of glue:


The parts list calls for a harness from the CDI unit leading up to the headstock area - this connects in the two handlebar switches.


Here's the finished stator:


Now I have the bike partly assembled, I can lay the harness out on it to see where the parts are routed and to ensure that I have sufficient length in each of the harness parts.


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