Thursday 30 December 2021

Motorcycle Electrical System Rebuild From Scratch

Researched links on re-wiring the 1971 Triumph Bonneville... 

The old Bonnie has an intact loom and many of the original electrical components, but many of these pieces won't have weathered the decades well and I'd be crazy to try and rebuild a hacked on electrical system in a fifty year old bike, so it's all coming out.  I'm going to take a page from the custom scene and build a loom from scratch and design and build a complete electrical system from scratch.

This ain't no modern digital machine so the electrical system in it is prehistorically simple.  Building a dependable replacement with quality modern upgrades (proper copper wiring, modern connectors, new electronic ignition and coils, etc).  The result should be a 1971 Bonneville that is more spritely and dependable than anything that rolled off the line in Meriden in 1971.

Tutorials on creating a motorcycle wiring harness/loom:

BikeExif Tutorial:

Rewiring tutorial:



Resource (costs 20 pounds):

Another good resource ($40):

I've purchased and read that last one - it's a gentle introduction to electrical work but I found it a bit simple and wished it had picked up speed as it went.  If you've never done any electrical work then it's a good place to start, but that's what I do all day so I was hoping for something with a bit more depth.

Replacement harness:

Prebuilt '71 Bonneville wiring harness:

Original loom wiring colours:
  • RED (seems to be earth but then battery + so this is a positive earthed bike?)
  • WHITE (headlamp loom)
  • GREEN/WHITE STRIPE (LH handlebar switch & main loom)
  • BROWN/GREEN STRIPE (headlamp loom)
  • BROWN/GREEN STRIPE (headlamp loom)
  • WHITE/YELLOW STRIPE (L/H handlebar switch) + ignition coil
  • BROWN (headlamp switch)
  • GREEN/RED STRIPE (L/H handlebar switch)
  • PURPLE (horn press R/H switch)
  • LIGHT GREEN (L/H handlebar switch)
  • PURPLE/RED (earth?) horn
  • BLACK/WHITE STRIPE (condesner pack/ignition coil split)
  • IGNITION COIL: BLACK/YELLOW STRIPE to coil & condenser pack + WHITE to coil
  • RED (earth frame)
  • BROWN/BLUE: Zenor diode
  • RED to battery positive (that doesn't make much sense)
  • BROWN/BLUE: battery negative
  • REAR LIGHTS:  BROWN/GREEN STRIPE (rear lamp)+BROWN (stop lamp)+GREEN/WHITE STRIPE (L/H indicator)+GREEN/RED STRIPE (R/H Indicator)+RED (earth)
  • STATOR (GREEN/YELLOW STRIPE+WHITE/GREEN STRIPE) were advertised in the UK's BIKE Magazine...

The Motogadget is an all-in-one electrical block for all electrical items on a bike - it also provides you with a bluetooth connection so you could start and stop it by your smartphone:

Not really what I'm looking for for the Bonnie project, though I'll keep it in mind for a future ground up custom build.

A new ignition barrel with keys looks to be about $80.  I'll see if Britcycle has them.

The existing wiring looks like it was taken apart and left that way - I'm tempted to take it all out and just rewire it rather than trust the old mess.

Electrical Systems Parts List:

  • Ignition barrel & key set
  • wiring to rebuild loom step by step - I'd need correct gauge wiring & connectors
  • fuse box
  • fuses
  • reg/rectifier
  • upgraded/modernized stator

Motorcycle wiring how to:  A commonly found writeup someone has done to walk any interested DIYer in how to rewire your bike.