Ignition Switch Bypass Relay - ST1100 Archive of Wisdom

[Piet]

Wondering if anyone has done this modification?
http://www.st-riders.net/index.php?topic=3643.0
I like the concept of what it is trying to accomplish.  I just wonder if its a 100% correct though.
I liked it for two reasons,
1.  Reducing the current through the ignition switch might extend the ignition switch life and in my case the ignition, seat, and pannier locks are all keyed alike so I do not want the ignition switch to need replacing anytime soon.
2.  The decrease in wire run due to the relay install should mean brighter headlights, less affected by indicator pulse, etc, etc.

So after buying the necessary I set to work.

I am no expert but I don't think they maximise the results. 
There are 3 Red/black wires that come from the ignition switch to the fuse box not just 2.  Please see the photo of the fuse box in the original post showing the wires in the rear.
The first supplies the two top fusses/circuits.
The second supplies fuses 3 & 4
The third supplies the bottom fuse the 7th fuse, the 20 amp headlight circuit.

The mod as described does not remove the headlight circuit from the ignition switch so no benefit to the lights and keeps the full headlight current through the ignition switch.  If you have done this mod exactly as described, i.e. You cut the 2 uppermost red/black wires etc. Try this to prove the point.  Temporarily disconnect the relay coil signal wire (disabling the relay) and switch on the ignition.  The headlights still work, don't they?

To my way of thinking it hardly worth the effort of the mod if you only go half way.  The top 4 fuses feed, (not in order ... Just reading the circuit diagram rather than looking at the fuse box)
Neutral, oil, temp, tacho, horn
Position, meter light, tail
Ignition, starter, alternator
Turn signal brake

How much better to include the headlight via the relay!
I certainly did by cutting the 3rd red/black wire and going through the relay.

One final observation of the circuit as described originally.
They put a 50 amp fuse inline.  I ask the question Why?  Every circuit in the fusebox already has a fuse.  A fuse is a necessary weak link installed in the circuit.  A fuse is calibrated so that at the specified current the resistance of the fuse is so great that the fuse wire gets redhot and melts.  So why add a second weak link when you already have every circuit protected by fuses?  To my way of thinking its not necessary.  The whole point of this is to keep circuit resistance to a minimum. 

I hope this is helpful, and I hope I am not way off track.

[Yorkie]

I agree totally with everything you have said, and I might add it will be possible with the original mod to get a back feed from the headlight causing ignition to not turn off the bike.

[alans1100]

Not sure if you've seen the modification wiring diagram or not.

The two red/black wires that are cut and then joined together power the fuses from A to E. One cut wire goes to C which is the headlight power feed and the other cut wire powers fuses A, B, D and E. The power feed for all five fuses now comes from the battery via the starter relay switch, 50 amp (total amps for 5 fuses = 60) fuse and a 70 amp relay. The power to activate the relay comes from the ignition switch

The original wiring has only a feed wire from the ignition switch, the starter switch, Hi/Lo switch and then separate relays for Hi and Lo beams. The modification (in red) removes the ignition switch from the headlight sequence with out doing any more.

That's how it looks to me on the wiring diagram

[Piet]

Hi Yorkie & Allan,

Yorkie.  Thanks for your comments.  I glad someone else found the same results.  I might have missed some thing however, as I cant see how the ignition error feed might occur.  Given the farkle was implemented exactly as described originally, leaving headlights running through the ignition switch, ... when the ignition is turned off the feed to the headlights is cut off removing batery +ve and at the same time the relay will drop out cutting off battery to the other circuits.  Where does the danger off a cross feed occur?  I am missing something.

Alan.  Thanks very much for your circuit diagrams, thats great.  In reply, the circuit is a simplified diagram of the actual wiring, it does not necessarily show every wire in the loom.  Its this that allows one to easily miss the fact that one wire does NOT connect to four fuses, The top wire connects to the top two fuses 1&2.  The lower wire connects to fuses 3 & 4.   The 3rd red/black wire is the bottom one and this connects to the 20 amp headlight fuse #7.  (Top, Lower and Bottom, refer to the red/black wires when you are looking at the back of the fuse holder.)
You can test this with a multimeter.  I disconnected the battery and pulled all the fuses and then confirmed each connection.
I also confirmed that the original farkle missed the headlight circuit by pulling the relay.  Now switch on the ignition.  The headlights still work because they are not in the relay path but remain under ignition switch control direct to fuse #7. That was the point of writing this up.  I wanted to alert friends to the fact that the headlight circuit was not included in this farkle.  Its easy to add it of course.