Undocumented spare +12V switched connection!

There’s a dirty little secret that the CBF125 has been keeping from me and I’ve tapped into it. Behind the left front cowl, amongst the wiring, there’s a clear piece of tubing containing one lone female bullet connector crimped to two blue/black wires. The ONLY blue/black wiring on this bike is found on the live +12V output from Sub Fuse B – which is responsible to supplying power to the ECU, sensor unit, fuel injector, fuel pump and ignition coil. So why not crimp a male bullet connector to the positive feed of a low powered accessory (such as a GPS!)?

Well that’s exactly what I did. You may recall my previous method of connecting my TomTom Rider charging cradle via a piggy-back blade fuse connector. Since the TomTom Rider is rated at 1A at 5V, this works out as 5W. I would also imagine that 5W is the maximum amount of power that the Rider will use, and most of the time, it will probably be consuming less. The charging cradle lowers the 12V from the bike’s electrical system to 5V for the Rider. Current draw from the bike’s 12V electrical system will be about 0.42A – which is very small.

The two Sub Fuses on the CBF125 are rated at 10A each and I very much doubt that the components fed from Sub Fuse B are drawing anywhere near that amount of current. I have no way of working out exactly how much loading is on that circuit, as the power ratings for these components is not published. One way to get a rough idea would be to substitute differently rated fuses (5A, 7.5A etc) in steps, going lower, until you find one that blows when the bike is running, then you will know that the current draw is roughly somewhere between the rating of the last fuse you tried and the fuse before that. I haven’t done this (yet).

Here is where you’ll find this stray bullet connector:

The clear plastic tubing is taped at the top – you just need to peel off the insulation tape in order to get to the connector, with no need to cut the clear tubing itself. The red wire is the positive feed to my TomTom Rider cradle (I have removed the original piggy-back fuse connection). If you do want to power something more substantial from here, such as heated grips, or a 12V cigarette lighter socket, you should use this connector to trigger a relay that switches another feed directly from the battery. You then have the possibility of making up an ‘accessory box’ that can have multiple fused outputs so that you can connect up lots of things! Setting something like that up is beyond the scope of this article and since I don’t require something like this personally, I shan’t be dwelling on the subject.

Anyway, as they say, the proof of the pudding is (look at the top right of the LCD)….

As for Sub Fuse A, we do know the wattage for the lights that are fed from it, and using that information, we can work out that with a pair of indicators (2 x 21W), all 3 warning lights (3 x 1.7W) and the brake light (21W) on, we have a maximum power usage of 68.1W on this circuit. That’s a current draw of 5.675A – so we have plenty of headroom before we hit the limit of 10A imposed by this fuse. It is possible to even swap the indicators for LED units (as well as the flasher relay for one that can handle low resistance LED’s), that draw only a few watts, which would easily allow you to run heated grips, that typically draw 3 – 4A, comfortably from this circuit, via a piggy-back blade fuse connector.

Remember that the main fuse on the battery is 15A and this represents the maximum current draw of devices connected to both Sub Fuse A and Sub Fuse B.


23 thoughts on “Undocumented spare +12V switched connection!

  1. another gr8 post 😉
    i just bought some led indicators from ebay,do you think i would need to change the relay??i was hoping just to connect and go

  2. Hi,
    im not amazing with the electronics of a bike so iv wired my heated grips straight to the battery, so they can be left on with the ingnition off 😦 , but does this mean i can connect them straight to these wires without any problems ??? thank you very much 🙂

    • I would be careful as heated grips draw quite a lot of current. You may get away with it or could start blowing fuses/melting wires. The other option is having a relay that is switched by that live feed, providing power from the battery directly. That way you don’t place any load on that circuit itself.

  3. Hey, nice find!

    I have just finished crimping my cables to that wire but I was wondering what/where would be a good place to ground them?

    Thanks Harrison

  4. Ran a wire from battery to the front of the bike, working great!

    Just got a nail in the tyre this morning, dammit.

  5. Hi, great blog! I take possession of my new cbf 125 in January and I have a question, I don’t know much about bikes or cars in general I seen something called ultimateaddons for the iPhone 4 waterproof and wires to the battery (so I can see the tomtom app and no battery drain) will it be compatible with the cbf 125 new model? (with rev counter) and a brief explanation of how to fit would be greatly appreciated! Thanks a lot!

  6. Fantastic Blog, have spent the last hour reading your posts!

    Do you have photos of the mounting of the GPS to the handlebars? Interested to see where you mounted, interested in a similar setup for here in Mexico City.
    Thank you!

      • No probs. Have found these really good grips, for the 25 quid price tag you can’t fault them. The clutch side handlebar needs insulating though, I used heatshrink tube, as the bar end and weight sucks out the heat!!

  7. Hey i am wondering if this blue wire is swtiched via the ignition..? and what do you recon the max ampage draw is possible through this hiden wire, I am thinking HID, Or have they changed the front headlight to DC now on new models, I have ordered a HID kit and looking over the net for best way to fit it.. Your views would be greatful.

  8. Hi, I plan on connecting a relay to this connecton, that will switch on a DC circuit wired up directly to the battery. I would like to run heated grips off it but also to connect up the headlight, dash lights etc that are currently on AC so i can put some better LEDs and a HID buld in the headlight. Is there a place you know of where the cable powering these lights can be cut in one place to switch them to connect to my DC circuit? I may need to look at the wiring diagram and follow the cables to try and work it out, there quiet hard to follow!


    • Ok, think i’ve figured it out, the yellow wire coming out of the rectifier is supplying power to the lights, if i cut it there and attach it to my DC circuit i will be good to go.

  9. ive bought some red led light to go under my bike how do i connect them up to my bike do i need a transformer or will i be ok just wiring straight to battery

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