Sfc1000 fuses and what is this purple wire?

SkinnyPinny

SkinnyPinny

Full member
Location
Cambridgeshire, United Kingdom
Hi all, I have blade fuses in place of the original ones, 1 x 25amp and 2 x 7.5amp, The headlight/taillight fuse blew half way into a 125 mile ride. So back at home, I started checking the connections at the fuse and headlight, cleaning the connectors etc, when I found this purple wire loose in the plastic sleeve behind the headlight.
So, questions for you lot please,
Am I ok to put a 10amp fuse in the headlight/taillight, original was 8 I think, I can’t get 8amp blades so went with the closest, ie 7.5 and what exactly is this purple wire, which goes to the temp gauge? what does this diode do and is it needed? Thanks for any help, Stuart
 

Attachments

  • image.jpg
    image.jpg
    127.7 KB · Views: 43
My first thoughts are that the resistor is there to reduce the voltage to whatever it’s connected to, so don’t bypass it without checking. Is it standard? (I can’t remember one on my RGS).
For the fuse, 7.5 is safer, but 10 is fine if your wiring is good for it. The main problem is what caused it to blow… loose wire touching the frame? Bigger headlight bulb? New LED tail lamp faulty? Does it happen often? Has the fuse lasted for years or is this the first trip with the new fuse block? Fuses can simply wear out, especially if they’re running close to their rating, so it could just be a one-off. I’d look into the total load on that fuse and go from there, could be indicators etc on it too, and it all adds up to total load. If someone has replaced the fuse block, maybe there are relays too and possibly too much load has been transferred on to the fuse that’s blowing.
Sorry, no specific advice 😉 but you could just hook everything back up again and bung in another 7.5 fuse to see if the problem repeats. That would be considered as research 👍
 
ok, as far as I know, this is as standard,
I have had the bike 15 years plus, but only just started using it again after being in storage for a while,
The temperature gauge has never worked, by that I mean when you switch on the ignition, the needle flickers, but that’s it, it never moves. I’ll see how a new 7.5 fuse goes, thanks,
 
SkinnyPinny said:
ok, as far as I know, this is as standard,
I have had the bike 15 years plus, but only just started using it again after being in storage for a while,
The temperature gauge has never worked, by that I mean when you switch on the ignition, the needle flickers, but that’s it, it never moves. I’ll see how a new 7.5 fuse goes, thanks,
Click to expand...
Yep good. Since it's been ok in the past, maybe it just wore out. I always prefer the simple answer first, before disassembling the whole loom ;)

Sorry can't help with the temp gauge...
 
Run a multi meter between the purple and earth with ignition on and off and see when or if it makes a circuit. If the gauge doesn't work just tape off to isolate the metal connector
 
well all seems ok at the moment, all lights work, the resistor is connected again as I assume it should be there, the purple wire runs outside of the plastic sleeve now, maybe a bit vulnerable but we will see, thanks for pointers,
 
SkinnyPinny said:
well all seems ok at the moment, all lights work, the resistor is connected again as I assume it should be there, the purple wire runs outside of the plastic sleeve now, maybe a bit vulnerable but we will see, thanks for pointers,
Click to expand...
You may as well insulate the purple to avoid any poss of a short to frame/shell.
 
I don't have any knowledge specific to the SFC1000 wiring, but low wattage resistors like that are typically wired in series with LED components like indicators, tail lights etc.

It's not part of the headlight circuit because it's too skimpy. It may be the power feed to the tail light if that is a LED type lamp. The resistor colour code indicates that it's a 100 Ohm resistor, which is in the ballpark for a LED series resistor (can vary a lot depending on the current rating and number of LEDs used).

I don't reckon it's factory original because LED automotive lights weren't commonly installed by manufacturers until after the last Breganze bikes came off the production line. So if it does indeed have a LED tail light, then I very much suspect an owner modification at some later stage, especially since the installation of the resistor was done in such a crappy fashion. It would be a way neater and more reliable joint if you shorten the wire tails on the resistor, slide a piece of heat shrink tube on one of the feed wires then solder the resistor in place. Slide the heat shrink back over the joint and hit it with the heat gun to shrink it on tight.

The reason for shortening the wire tails is that they're solid wires rather than braided, so they are less tolerant of movement due to vibration than flexible braided wire. Cutting them short reduces the likelihood of them bending all over the place while in service. The heat shrink sleeve will also help support the joint. It looks like that's why it broke in your photo. There appears to be a small broken stub if wire in the crimped sleeve.
 
Yes I wondered that Cam, but it's been confirmed that it’s definitely the temp gauge, and that corresponds to the usual colour coding. I now think the resistor might be for calibration of the gauge. If so, it could be removed, or at least tested to see if that’s the problem with the gauge 👍
 
The resistor appears to be 100 ohm, 250mW. Max current flow is 50mA, so it can't be feeding anything that requires a substantial current flow.

bazzee
 
Quote “could be there to 'fudge' the temp. gauge reading?”
That’s exactly what I now think, my suspicion is that it has been broken since ever, as its a crappy fit and the temperature needle has never moved. I’ll see if it works next time out, otherwise I’ll just replace the whole wire,
My main worry was 7.5 or 10 amp fuse,
Again, I’ll see what happens next time out,
Incidentally, I have no LEDs, all standard bulbs, thanks for all the suggestions, always helpful, Stuart
 
Nice one. Adding a resistor is a normal way of correcting an inaccuracy, but it’s a bit curious that it was needed. When you found it, was there a bare end bouncing around? Because that could be what blew the fuse 🤔
 
To check the instrument, simply ground the sensor wire, the needle should flick to "max". The resistor is not a stock fitment. In stock form, the purple wire would be in the sub loom for the instrument panel instead of flapping in the breeze. On both the RGS and SFC, the needle will only raise from the OFF if ambient temps are around 40°C or during sustained high speeds at ambient temps above 30°C. Thoroughly superfluous imho.

piet
 
there was a time when the RGS loom was used which had an electronic tacho, the SFC has a cable driven one?? the first SFC1000 had Smiths clocks both cable driven, and that was the subject of a recall to fit the white faced vague liars. cant recall, exactly but you get my drift I am sure, and this may have been the wire for the tacho, most were incirectly sent out not insulated, very sloppy from factory! someone will know more than me.
CLEM
 
You must log in or register to reply here.
Back
Top