hi , doing a cafe build, new speedo and learnt the robmacks posting about need to wire in 2 x 2w 56 ohm resistors from wire 6 to wire 9 in the cluster. Really basic question I know but do resistors go a particular way? Seem to remember something about the lines on them. And is this fix just solder wire to resistor, solder on another resistor and connect to wire 9, then heat shrink the lot?
The understanding is that this resistance kicks in the alternator to charge and will not do this otherwise.
Apologies for what feels like dumb questions but have to start some where.

I don't have the answer for you but don't feel any question is dumb. Knowing to ask the question is anything but being dumb!! I suspect you are right in that it causes the alternator to kick in.

Someone will have the right answer here and good luck with it too.

Resistors can be fitted either way, similar to a fuse that can also be fitted either way round.

+1

Now if you were putting a bunch of resistors on a circuit board you would want to orient them the same way to avoid having to flip the board around to read the band's....

Phil, I'm the king of stupid questions/actions on the forum here.  Everyone is very understanding and willing to help. I've been both astounded by and very grateful for all the help I've received here.  

On this alternator issue, what I did was wired in a Radio Shack "12v LED" part no. 276-270 that has a resister built into the light ("12v LED" is in quotes because, as I understand it, it's not a true 12v LED, rather its an LED that works in a 12v system due to the resistor).  That way I have an LED that tells me whether I'm charging or not.  On my cafe build, I used a K1100 fork that had a small hole in the top triple clamp where the light fit perfectly in the recess.  Very clean and unobtrusive, if that's the look you are going for.

heres  a thought to maybe some edumucation ...lol

a resistor resists current flow ...it is not polarised ...so doesn't matter much which way it is installed

when we start talking about other electric things ...many are polarised and only work one way ...such as a diode ...an led ...a transistor

but not the old resistor   ....but there is another consideration ....what wattage resistor  is specified ?

there are tiny ones rated at 1/4 watt ...and others rated to 5 watts and more

ill guess that  a 5 watt resistor (looks a bit like a square long ceramic brick with wires out the end )

might be the one you are looking for ....not much over 50 cents each from any good electronics retailer

these things with solid copper (tin plated leads ) do require some mounting to prevent vibration working at fracturing the leads

good luck hope it works out for you

Thanks guys for the help, what I have done is put a red led between 6 and 9, an idiot light which is what I was putting in my new console anyway. I believe this will create some resistance?? I will keep an eye on my battery charge and if alternator doesn't appear to kick in will put in additional resistors as per original plan. Sound reasonable?
Ta

Someone correct me if I'm wrong here, but I can't see how this will work with an LED. Current needs to flow in either direction.

Hmmm...wrote a longish reply, but it doesn't seem to have posted. So, here's the shorter version:

I don't know if this is a situation where an LED (a diode) would cause trouble by restricting current from flowing one direction where both directions are necessary to "excite" the alternator for it to function.  Surely someone else on the forum will know and can chime in.

In my case, my alternator was working without a light/resistor.  Another knowledgeable form member told me that it was likely this was due to there being residual charge in the alternator, but I was lucky it worked at all.  When I heard that, I put in the LED/resistor combination for good measure, just to be safe....without giving a thought to the diode issue.  I've heard stories of others having my experience (it working without a light/resistor) and the opposite (no light/resistor, no charging).  Since my light/resistor combination worked exactly as the stock incandescent light did, I figured it was a workable solution.  

However, thinking about it now, my conclusion doesn't necessarily follow as a matter of logic (that being more my expertise, as opposed to being knowledgeable about electrics, which I'm not).  Given that I was charging without a light/resistor, my LED/resistor combination may not be the cause of my successful charging.  It could be that I'm charging due to residual charge left in the alternator, and that the LED is merely confirming that I'm charging, but not causing it.  

Very curious to hear what other, more knowledgeable members have say about this....

Thanks guys, my head is starting to hurt, but will get to the bottom of this. So my understanding thus far. Having connected wires 6 and 9 with an LED in line may work, if it doesn't work I will ride my bike and slowly flatten the battery. I have a 50km ride to work so don't want to get stuck there. Or I could put in a red incandescent as per original cluster or I could put in the two 56 ohm resistors as per Holister, or the red led resistor combo.

Occasionally the alternator will start to charge without any current due to residual magnetism left in the rotor (this should not happen but the years take their toll) which will make the alternator "self excite" but most of the time this wont happen.
The current that flows when the led/bulb is on will cause some magnetism so the alternator will excite and the more current that flows up to about 0.25 Amp the lower the speed at which that will happen.
A typical LED will flow about 20ma or 0.020Amp and a 3 watt incandescent bulb will flow the 0.25 Amp required for optimum effect.
Usually charging starts at around 1200rpm using the OEM incandescent bulb but using a LED can cause the initial excitement to be delayed till about 4000rpm, however once the initial charging has happened all will work as it should.

Phil63 wrote:hi , doing a cafe build, new speedo and learnt the robmacks posting about need to wire in 2 x 2w 56 ohm resistors from wire 6 to wire 9 in the cluster. Really basic question I know but do resistors go a particular way? Seem to remember something about the lines on them. And is this fix just solder wire to resistor, solder on another resistor and connect to wire 9, then heat shrink the lot?
The understanding is that this resistance kicks in the alternator to charge and will not do this otherwise.
Apologies for what feels like dumb questions but have to start some where.

Hi Phil, I've almost finished my cafe racer but I'm having the problem of the alternator not charging my battery, another K100 rider suggested the OEM cluster once removed needs globe or LED to " excite " the alternator to start charging. I've come across this old post......did you get your's fixed ? if so would you mind sharing some pics and a description of what to do ?  Andrew P

I just came across this rather old thread but the info is rather empiric, so since this is technical reference as well as an individual's problem I'll add a few notes.

Although the alternator produces A.C that comes from the rotation. The magnetic field is of constant polarity and is exited by a direct current.

The little incandescent bulbs are usually 3W , so draw about 3/12 = 0.25 amps from 12V ( the winding resistance will much less than 1 ohm and insignificant by comparison ). 

LEDs are rated by power ( mW) , not voltage.  The common 5mm ones you likely want to use to a bulb are typically 20mW.

They do have voltage ratings : max reverse voltage may be as little as 6V, so don't be tempted to work out which way round by trial and error.  Many will block 12V but it is not guaranteed by the spec.

Forward voltage drop is about 2V for the red ones. So current flowing will be ( 12 - 2 )V / resistor.  A standard 470 ohm resistor will give about  20mA = 0.02A . That is the nominal conditions for producing light but they can handle a bit more before they burn out but if they are not in an air flow I would not push it too much. If well cooled you double that but may not like that much light in your eye whilst riding.

So as Rick G correctly pointed out above they will produce much less initial excitation field and the alternator will need to spin a lot faster before it kicks off. This will not mean that it drops out earlier at low revs since once running the output if fed back internally to excite the coil.   That is why  they bulb goes out : there is 12 V on both sides of it and no current flow.

If the bulb starts to come on and glow when running that means the output is dropping badly and you have a charging problem.