Yamaha RXS100 12v Conversion

Introduction: Yamaha RXS100 12v Conversion

About: I live in Devon, England, with my partner, who is a motorcycle tuner. We like recycling, re-using and repairing, and share an appreciation for old machinery - we've restored several old lawnmowers for the plea…

Okay, this is my first Instructable, so be nice please!

How to convert your Yamaha RXS100 from 6v electrics to 12v electrics.

Why? Well, the RXS is a cracking little bike but the 6 volt electrics really let it down. Do this conversion and you'll have no more issues with dim lights, dim- to non-existent indicators, and the headlight dimming whenever the indicators flash. No more revving the living daylights out of the bike just to keep your indicators visible!

It's actually pretty easy - I'm no bike mechanic but if you can work a soldering iron (doesn't have to be neat!) you can do this. And it's so worth it. There is a video tutorial available by Dave Haney, which will get you as far as the soldering - watch it by all means, it is very useful, but I wanted to do something that includes every step, especially the reg/rec wiring - and gives you a shopping list to boot.

You will need:

A new 12v battery that will fit in the space the old one went in!

A new reg/rec

A new flasher unit for the indicators

New bulbs all over, so that's dash, headlight, indicators and rear.

A relay (this is to stop the headlights staying on - when you do this conversion, the lights are powered directly from the battery. You can skip the relay - but if you do, you'll be able to leave the lights on when you turn the ignition off, and at some point, despite your best intentions, you'll flatten the battery.)

Tools you'll need:

  • Soldering kit
  • A flywheel puller (generic Yamaha one)
  • A flywheel holding tool
  • 12mm socket and wrench
  • 19mm socket
  • A breaker bar (optional)
  • A magnet-on-a-stick (the telescopic things you get in some toolkits - these things can be lifesavers! Optional but useful)
  • A plastic tub (for your bolts/screws/bits - so you won't lose them)
  • Basic tools to get to the stator plate and change your bulbs etc
  • Patience.. give yourself a weekend if you're not a mechanics whiz. If you are, you probably don't need this Instructable!

Step 1: Go Shopping!

Here's your shopping list - that famous auction site is where I sourced everything except the reg/rec. You can just copy/paste these descriptions into the search bar.

Get a flywheel puller if you don't have one. Yamaha ones are all the same, as long as it's 27mm LH thread it'll do.

Battery - this is what I used, it is a snug fit but will go:

POWERSONIC PS-1242 12V 4.5AH Sealed Lead Acid SLA Rechargeable Battery 18-1712


Dash bulbs: CAPLESS 12V 3W LIGHT BULBS 504 (you can get a box of 10)

Headlight: P45T HR2 12v 40/45w

Rear Light: 12v 21/5W BAY15D Stop/Tail bulbs, come in packs of 2

Indicators: 12v 21W BA15S (you need 4!)

Regulator/Rectifier (should be a 12v 5-wire one, this one is commonly used and it works fine)

Flasher relay - make sure it's 21W, 12v. A 3 pin one will work.

12v relay for the headlight. 4 pins, 40A will work.

A fuse - 10A should be fine, this might already be what's in there.

Some bullet connectors (get decent quality ones, crimp-on jobs will fall off)

Step 2: Remove the Flywheel and Stator Plate

Let's get the scary bit out of the way first. We've got to get to it, though, so remove the seat (2 x 12mm bolts near the back) and then the petrol tank (turn off the fuel tap, remove the hose from the carb - just tug and wiggle - and then undo the 12mm nut). Take off the gear lever. Remove the flywheel cover now - the whole thing, not just the round bit. Let the cover dangle from the clutch cable, or stash it on top of the bike out of the way. Take the side cover off (one screw) left side (covers the oil tank).

Now you have to get the flywheel off. You need your flywheel holding tool for this. Two pairs of hands is useful here so rope in some help - you can do this alone, don't panic, but it can be a faff.

Undo the big central bolt from the flywheel. Wedge your holding tool to hold the flywheel still (or hold it) and undo the big bolt (19mm socket, a breaker bar may help). Get the two washers out too and note the order they are in (nut, then spring washer, then flat washer underneath). If they are tricky to get at, a magnet on a stick works a treat here.

Now screw the puller into the flywheel. Make sure the central bolt on the puller is undone as far out as it goes, then screw the puller into the hole in the middle. Remember this is a left hand thread, and it's fine as well so don't cross thread it.

Now hold the whole lot still (this is why you need a spare pair of hands, or wedge the flywheel holding tool against the footrest or the floor) and screw the central bolt on the puller in. This pushes the flywheel off the end of the crank - you will hear an alarming "crack" when it goes.

IMPORTANT - There is a tiny bit of metal on the crank that lines up with a groove in the flywheel. This bit of metal is called the Woodruff Key. DO NOT lose the Woodruff Key. Generally they stay put anyway, but sometimes they drop out, watch for it and don't lose it!

Remove the puller. Now you can remove the flywheel - it will just pull forward, but you will need to give it a tug because there are magnets holding it in there. Now you can see the stator plate with the coils in place.

The stator is held in with two screws (top and bottom), remove them and pull the whole plate towards you and off.

There is a neutral wire coming from the body of the bike to the stator. Undo it - it's just a spade connector held on by a screw, underneath the rubber cap.

You can leave everything attached here, if you like - if you are lucky enough to have a comfy indoor workshop or garage to work in then don't bother undoing all the wiring, you may as well do your soldering next to the bike and save yourself some work.

Step 3: Rewiring the Stator Plate

The trickiest, and of course the most important bit, of the whole operation is the soldering on the stator plate. Yamaha have been really kind to you with the RXS - you can't do this conversion on a lot of bikes.

The stator plate is the bit that takes the physical motion of the flywheel and converts it into electrical energy.

On the stator are 3 coils. The little one is the ignition pulser - this is what times the ignition. The medium sized one is what generates the energy for the spark itself. The biggest, bottom coil is what generates power for lighting and charging.

Originally on the RXS this coil does two jobs: it charges the 6v battery and it runs part of the lighting circuit via the centre tap (like a little extra winding round the middle of the coil). What we're going to do is use the whole coil, rather than just part of it, to charge the battery, and the lighting system will then run off your battery. This means your lights aren't reliant on how fast the engine is turning - no more dim lights at low revs!

Basically you are getting rid of the centre tap, so you have to make two soldered joints - one to link out the centre tap wires, and one to join a couple of other wires together.

Cut the Y shaped joint between the centre tap and the 2 wires going to each end of the coil.

Take the two wires from each end of the coil and solder them together. Cover the joint up with a bit of heatshrink or electrical tape.

Snip the black earth wire on the front of the stator and push it through to the back. Solder this to the yellow wire that used to go to the centre tap. Again, cover the joint with tape or heatshrink.

Please excuse the screen grab - I did have pics but they are lost in the mists of time!

Step 4: Finished Stator Plate

This is how it should look when you're done soldering.

Two joints - one between black and yellow, and one between the two coil wires.

Reassemble the stator/flywheel (remember to line up the Woodruff Key with the slot in the flywheel) and put the cover back on. Don't forget the washers behind the flywheel nut (flat, then spring washer on top). Tighten the nut up properly using the flywheel holding tool to hold everything in place. Remember to reconnect the neutral wire.

Step 5: The New Reg/Rec

The old reg/rec (regulator/rectifier) is redundant now. We've got a new one to go in its place so remove the old one.

Fit the new one on top of the air box - see photo. You've got to squeeze in a headlight relay in this gap too, but it does all fit!

There is a bundle of wires coming up from the engine:

  • Red & White Striped wire - goes to the CDi for the ignition timing. Leave it alone, it's not relevant to what we're doing.
  • Red & Green Striped wire - This used to be the 6v charging signal, it now goes to pink and forms half of the 12v charging circuit, via the new reg/rec.
  • Yellow wire - This used to be the 6v lighting signal but is now the other half of the 12v charging circuit, and goes to yellow, into the new reg/rec.
  • Pale Blue wire - neutral, leave it undisturbed
  • Black wire - earth, leave alone
  • Black & Red wire - ignition power, leave alone

Out of this bunch, four wires go into a block connector - green/red, yellow, blue, black. Leave the blue and black wires where they are, but snip the green/red and the yellow off at the block and fit bullet connectors to them. Using the bullets, connect these to the new reg/rec - red/green goes to pink, and yellow goes to yellow.

Coming out of the regulator:

  • Pink wire - to green/red and off to the engine
  • Yellow wire - to yellow, and off to the engine
  • Red - 12v output (connect to existing red battery wire)
  • Green - earth or -ve (to frame)
  • Black - voltage sensor (connect to brown, which is post-ignition live)

Step 6: Replace the Indicator Flasher Unit

This is a straight replacement - swap old for new. You can find it just under the top frame rail - find the spark plug and look above it. It hangs off a rubber whatsit.

Step 7: Add in a Relay

Because the lighting circuit now takes its power from the battery only, it is possible for you to leave the lights on when you turn the ignition off. Bad idea, because at some point you'll forget to switch your lights off (whoever does, anyway?) and then you'll have a flat battery and no lights when you need them.

So what can you do?

Easily solved. Fit a relay that switches off the lights when the ignition goes off.

You don't have to do this bit, but I don't know why you would get this far and not do it! Just wire the relay as per the diagram. Purchase details for a relay are in the Shopping List at the start of this Instructable.

The yellow wire is left over when you remove the old lighting regulator (pictured) - found under the seat and held on with 2 screws. The yellow wire heads off into the loom, but you can just re-use it.

You do need to splice onto a brown wire that is part of the loom (make sure it's light brown, not dark brown - the darker brown is an indicator wire and it's easy to confuse them - you can use a multimeter to check if you need to, you should get 12v on the brown wire all the time).

You can splice onto the brown wire using a sharp blade and cutting the insulation, soldering to the wire and taping up, or use crimp connectors.

Step 8: Replace Bulbs

Replace all your bulbs with the 12v equivalents, as detailed in the Shopping List.

Most bulbs are dead easy on the RXS, they are just a matter of undoing the lenses, but the dash bulbs are a bit fiddlier. Take the headlamp lens off, then remove the front indicators which will allow the headlamp bowl to fall forwards. This gives you access to the base of the instrument cluster, from here you can undo screw to get to the base of the instruments and change the bulbs.

Step 9: Fit the Battery

You may have to tweak the side cover - we had to cut out a notch around the battery but this does help to hold it in place. Make sure the terminals connect tightly otherwise they might drop off when you push the battery into place.

Step 10: Test It Out!

Test the charging voltage. You should get around 13-14v coming from the engine to the battery when the engine runs, regardless of RPM.

Test between the red wire (normally +ve to the battery) and an earth (in bike terms, earth isn't really "earth", it's basically the -ve side of the battery and any part of the frame should be earthed, but use a known earth point if you can).

Then test out the lighting system which should now work without the engine running. Check that the brake light works for both front and rear brakes, and make sure both indicators are OK. Check headlight on normal and full beam.

You're all done.

Thank you:


Yammy100 forums

Dave Haney

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    Question 3 years ago on Step 10

    Hi, i understand that this post is kinda old but hoping for your reply. Can I also do this mod with the YAMAHA RS100 stator?


    4 years ago


    With regard to the lights,do we need to connect the yellow wire from the lighting regulator to a brown wire to get any lights......we might not use the relay but at the minute,there's no lights at all......we did this today....got brake lights,horn.indicators and parking lights but no head or tail light :(

    Also,the soldering was a nightmare....it flatly refused to stick to the wires...just kept falling off in lumps......we tried to use bullets to connect the wires but there's no charging of the battery...help


    Reply 3 years ago

    hi , i know its been a year but did you sort it out , im exactly in the same position you were. cheers


    Reply 4 years ago

    If you omit the relay, then yes you would bypass it by joining yellow and brown. IMHO though it's a sensible addition otherwise it's too easy to leave your lights on by accident!

    Do you have no voltage at all on the red wire for battery charging? Should be 13 or 14v when the engine is running. If there's nothing, perhaps you have a different model reg/rec and the wiring's different, or the reg/rec is faulty. Or conceivably a poor earth?

    If you are struggling with solder sticking - give the wires a really good clean up first with some wet/dry paper, and a wipe off with contact cleaner or flux. Solder won't stick or flow onto to greasy wires. Then tin the ends first before you try to solder them together.


    Question 3 years ago

    hi , as a previous post i too have no lights. indicators , horn , neutral light/ oil lights, brake light all work . i have no brown wire in my loom , i do have the indicator brown wire . i have found a live wire on a brown wire in a blue connector block in the headlamp so i tapped into this for the black wire from the new regulator .

    stator plate all done

    so i have new regulator - pink to red green from engine , yellow to yellow from engine, red to red , green to bat neg. red to red bat. +

    i have bought 2 regulators incase 1 was duff.

    i still have no lights



    4 years ago on Step 4

    El rojo verde, donde queda conectado ?


    Question 4 years ago on Introduction

    Hello sir I'm already having a 12volts electrical system on yamaha rx100 but the lighting is not good. Can i also use this modification to charge battery better and put headlight on battery.


    4 years ago


    Will this work on the Honda H100 S II that i've just bought...the wiring looks similar but I do not want to start snipping wires if it doesn't work



    Reply 4 years ago

    I don't know - have a mooch on owner's club messageboards. I would imagine that it depends on what voltage the stator puts out; the Yammy one only outputs 12v once you do the wiring tweak to it. Whether the Honda one is the same, I couldn't say, but someone out there must know!


    6 years ago on Introduction

    Great first Instructable.....will be using this on my KC100 at some point in the near future......Thanx for sharing, and looking forward to your next :)


    Reply 6 years ago

    i was looking at this post with intention of converting my kc100.. did you take the plunge age were there any gotchas?


    7 years ago on Introduction

    Done this to a couple of bikes in the past, the improvement in lighting is amazing. Now you can fit led bulbs, this will reduce load on your electrical system further.

    Well done.


    7 years ago on Introduction

    Nice work on this tutorial!

    I had an old Yamaha similar this several years ago... so this brought back memories. Still miss that little bike!