TOPIC:

It seems at the moment this topic is coming up again and again, it makes complete sense but I wandered how many of us understand the rational behind this common modification.
Anyone who has read any of my posts regarding electrics will know that "Wookie keeps banging on about corrosive resistance" and this post will be no exception. It was common on all mass produced vehicles in the 70's and 80's to use barely adequate wiring ( both quality and gauge) Ford Europe were particularly bad for this and fitting upgraded headlight bulbs in a Capri or Escort would often burn out the wiring, light switch and dash loom !!!
Now 40 plus years on age has taken it's toll on that wiring with corroded connections, corrosion between the wire itself and the crimped connector and also those connectors loose spring tension over time.
Below is the igniter for my 82 Ltd and the wiring has age hardened ( you can see the cracks from bending the wire) each one of those cracks will allow moisture to get into the cable and start corroding it) eventually if left there would be green powder deposits around the crack and the circuit would stop working.
The perfect answer for all of us would be a full "re-wire" but that is a big and expensive job which in most cases is uneccessary, a small amount of corrosion will cause volt drops but as long as they are small they won't effect the operation of most electrical consumers ( remember they are designed to work at 12v and when the engine is running the system voltage is around 13.5v so there is some wriggle room)
When it comes to the coil feed this is also largely true ONCE IT IS RUNNING but during starting (especially when cold) the system voltage can be as low as 9.5v to 10v. If you now add in a 1.5v volt drop your coil voltage is down to a little over 8v which is why you have a week spark (a 30% reduction in primary voltage will mean a 30% reduction in secondary voltage at the plugs)
This seems to effect coil voltage the worst as on a lot of these bikes the feed has to go through multiple connectors and switches before it gets to the coil (loosing a little at each on the way) By fitting the by-pass relay you are simply getting back to where it was when new before corrosion took hold and giving the coil full battery voltage
WARNING: if you have electronic ignition be careful, if you have 2 ohm coils and ballast resistors connect the output from your relay before the resistor (not between the resistor and coil) if not you will double the current you put through a 40 plus year old igniter which will problem mean a shopping trip 
If you already know all this apologies for boring you but if not, you now know why you are doing what you are doing

 

Below is the simplest diagram I've seen for adding a relay. (I've had it in my "to do" folder for a while now.)
I believe it's from forum user Wired George? 
Dyna S coils or standard OE, same applies.

 
 

We used to keep plenty of these in stock for our customers with British cars.

Good explanation and advice Wookie.  I have the bypass on my KZ1000 but in the interest of originality my Z1 is original.  

Folks, if your headlight seems dimmer than what you remember from back in the day....it probably is.

We've installed ignition bypass relays on all of our Z1's.  That decision was driven in large part by what we learned when we disassembled an ignition switch to inspect the internal rotary contacts while chasing a fairly severe voltage drop gremlin on the WHITE circuit on one of our '72 Z1's..

We also wanted to retain originality & not have to butcher an OEM harness.

Initially, we created a prototype harness.for the relay to get wire lengths & terminal genders right.  Then we bought some 4.9mm (5 mm in some catalogs) barrel terminals to match the terminals of the OEM Z1 wiring.  That led to purchasing & testing a few crimpers before finding one that really created a secure factory-quality crimp.  (Crimping of stranded conductors into terminals is a surprisingly detailed science within itself.)  The prototype harness is used repeatedly as a model from which to build the bypass relay harness that's ultimately placed in service.  Everything's plug-n-play.  No modification of the OEM harnesses required.  If a return to absolute originality is desired, the bypass harness is simply unplugged & the OEM connections can be returned to their original positions.

Good Ridin'
slmjim & Z1BEBE

wrote:

We've installed ignition bypass relays on all of our Z1's.  That decision was driven in large part by what we learned when we disassembled an ignition switch to inspect the internal rotary contacts while chasing a fairly severe voltage drop gremlin on the WHITE circuit on one of our '72 Z1's..

We also wanted to retain originality & not have to butcher an OEM harness.

Initially, we created a prototype harness.for the relay to get wire lengths & terminal genders right.  Then we bought some 4.9mm (5 mm in some catalogs) barrel terminals to match the terminals of the OEM Z1 wiring.  That led to purchasing & testing a few crimpers before finding one that really created a secure factory-quality crimp.  (Crimping of stranded conductors into terminals is a surprisingly detailed science within itself.)  The prototype harness is used repeatedly as a model from which to build the bypass relay harness that's ultimately placed in service.  Everything's plug-n-play.  No modification of the OEM harnesses required.  If a return to absolute originality is desired, the bypass harness is simply unplugged & the OEM connections can be returned to their original positions.

Good Ridin'
slmjim & Z1BEBE

Similar to what I did when I install the bypass relay. Can’t say I made a harness but I did buy wires to match factory colors. All new connectors installed matched OEM, mine is reversible if desired. 

I'll be installing an ignition by-pass relay within the next few days.
Are some makes of relays more dependable than others. I hate adding a possible failure point to the system.
This is the relay I ordered: {ebay.com/itm/385600026594}

I went with a Bosch automotive relay and pigtail. Legendary reliability. Has worked flawlessly for 10 years or thereabouts. If it ever fails then I can pull the relay and use a short piece of insulated wire with a male spade connector on each end (carried in jacket pocket) to insert in the pigtail so that the way the coil was powered is reconnected.

HELLA 4RA 003 530-001