SON SL dynamo hub wiring

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Joined: 8 Sep 2019, 1:23pm

SON SL dynamo hub wiring

Postby djugroop » 8 Sep 2019, 1:36pm


I have used and wired SP dynamo hubs with twin wires before but I am having trouble wiring my SON SL hub using coaxial for the reason highlighted below.

For those not aware SON do a hub that does not require plugs and makes contact with an insert embedded in the fork strut. This system is called the SON self connecting systems or SL for short. One end of the hub is live and the other end is the earth. So there is actually only one connector on the fork, not the hub on the live side.

I have the following:
- Tout Terrain Silk Road with SL fork
- SON SL front hub
- SON front light
- SON rear light
- All cable is coaxial.

My question is this. What do I do with the earth part of the coaxial cable that comes down from the front light as this is surplus to requirements (I think)? Do I just protect it by heat shrinking it up and ignore it? I did get it working temporally by connecting the earth part of the coaxial cable to the mudguard strut but this seems fiddly and in contrast to what the system is about (simplicity). And it would not work if I decided to run without mudguards, if I decided to put bigger tyres on etc. Plus it has stopped working altogether now, but I know that is probably down to loose connections.

I have tried and tried to find documentation on the SON site or Youtube videos which are normally very useful, but with this being a very rare set up I cant find s single thing on the subject. Peter White cycles touch on it, but not in as much detail as to the wiring.

Your help will be very much appreciated.
Dylan Jugroop

Posts: 35229
Joined: 4 Jan 2012, 6:25pm

Re: SON SL dynamo hub wiring

Postby Brucey » 8 Sep 2019, 2:56pm

you need a return connection from the light somewhere. If the light has a body ground connection then the return connection can be made via the lamp bracket and the fork, connecting to the hub locknuts. This is quite similar to the old wiring scheme for bottle dynamos. If using this scheme then all the places where there might be a layer of (insulating) paint need to be clean enough to make metal to metal connection reliably. If you do all this (with a suitable light) then the screen on the coaxial able is redundant; it can just be shielded with heat shrink.

provides some info for wiring. I would suggest that one good option is to run the coaxial cable from the lamp as far as the fork crown and then make a ground connection to the screen and lengthen the centre part of the cable with single core flex that will pass more easily through the fork blade. The cable splices can be hidden inside the base of the steerer (it is an excellent idea to leave the wires overly long and to secure the excess this way anyway; it more easily allows repairs should the need arise).

If you don't want to do this, you still want a wired ground connection and the coax passes inside the fork blade easily, then you can make a ground connection at the mudguard eye. If you use a bolt from the back, or a short length of M5 studding and some nuts, you can leave the ground connection undisturbed whilst removing the mudguards etc if needs be.