Author Topic: The strange green slug like resistor on the early Rd125!  (Read 1886 times)

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Offline Barnett

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The strange green slug like resistor on the early Rd125!
« on: February 10, 2018, 11:56:56 PM »
Thought I would post this here to maybe help clear up an obscure mystery that despite hunting everywhere and searching the net and Yamaha service manuals I could either find no answers or other mystified questioners. This is closely linked to Foy's post a year ago on early rd125 wiring looms.
Am at the stage of wiring up the as3 rd125 and could not figure out what the resistor that lives under the battery box is for, it appears only on some of the early rd125's and on the europa in particular.

Some of these bikes were fitted with a 4 position key switch, (counting off as position 1), and it is my belief that these were destined for mainland Europe and possibly Canada. The lighting is available via the handlebar lights on switch both in key position 2 and 3 and the last position 4 whereby you can withdraw the key, this last position being common to other switches with only 3 positions.
This threw me a bit as I thought pos1 off, pos2 ignition and everything else but no lights, pos3 as 2 but with pilot light on and full lighting via switch available, pos4 lighting only for parking.
The lighting function in position 2 is far dimmer than position 3. Everything is dimmer, including rear lamp and meter illumination lamps. Thought it was a wiring fault.

On inspection of wiring diagram for the europa, (which has mistakes in it, warning!),  Which shows the green slug resistor it appears the lighting circuit at the left handlebar switch has two power feeds, one being the 'normal' feed if I can put it that way which is activated when the key switch is in position 3 , the other the 'dim' feed, (Key pos 2). I.e. Two supplies wired in parallel.  There is no mention of why this should be in the books I have or the owners handbook.

On the post where foy commented, martin gave me the clue suggesting daytime running lamps.

So the first feed to the lighting position 2 is via the green resistor under the battery box. This resistor is of the order of 2-3 ohms and gets quite warm, (power resistor), cutting the voltage roughly in half and thereby dimming the entire lighting circuit, pilot, main and dip, meter lamps and tail lamp.
Switching to the 3rd position on the main key switch instantly brightens all lamps up as it is now feeding from the battery and not via the resistor. Interestingly the feed via the resistor is still in circuit, it is not switched out by going from pos 2 to pos 3, as it dosn't need to be as the lamps ignore this feed so to speak as its restricted and suck the juice from the unrestricted circuit instead.

So to those that worry about the resistor as theirs is broken either replace with any power resistor (60 watts say) at 3 ohms or so, (24/3/18 correction! After reading next post I rechecked resistor, it is stamped 0.8 ohms not 3 ohms), or higher if you want dimmer daytime or city lamps, or just unplug it at the resistor end, red wire or red with yellow trace. You will just lose the daytime running dim lamp feature on position 2, everything else will be as normal and work fine.

One wiring diagram shows all the wiring in place for the feature but no resistor, so you may have a four position switch but no city or daytime lamp feature anyway!

As to why a uk bike has this feature I have no idea as apart from the pilot lamp at the front and tail lamp there was no requirement for city lights in the uk at the time.

Was this a requirement in France or Holland? Who knows.

Sorry for long post and I expect many eyes have glazed over but may be useful to someone like me that was searching for an answer on this topic!

Below is a pic of the little rd progress to date!
« Last Edit: March 24, 2018, 10:04:14 PM by Barnett »

Offline 5port

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Re: The strange green slug like resistor on the early Rd125!
« Reply #1 on: February 15, 2018, 09:01:05 PM »
Good info!  Thanks for posting.  ;)

5port
5port

Offline AlanRD

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Re: The strange green slug like resistor on the early Rd125!
« Reply #2 on: March 24, 2018, 05:11:49 PM »
I do not have any knowledge of the RD125. But, on the Kawasaki Z650 & KH 500 (1976/77) manufactures fitted a 0.5 ohm resistor rated @ 20 watts on the European bikes to reduce the brightness of the dipped main headlight.
The USA model had a sealed beam lamp 50watt high beam/35watt dipped beam
The Euro model had a dual filament lamp 45watt high beam/40watt dipped beam...the resistor was fitted to reduce the dipped beam brightness.
 Not sure why, or who would notice...MOT requirement?   (parking/city 4 watt lamp was also fitted in the Euro bike headlamp)

Just curious, but the 3 ohm resistor seems a bit high, could it be 0.3-0.5 ohms?

Offline Barnett

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Re: The strange green slug like resistor on the early Rd125!
« Reply #3 on: March 24, 2018, 10:08:19 PM »
Alan, you are absolutely correct, I have modified my post above, rechecked resistor it says 0.8 ohms on the body, all be it very feint. Thanks for pointing that out.
Yes I also have a z650b1 and it also had a resistor in the lighting circuit, under the tank I think, previous owner had ripped it out, which was a common mod to improve the lighting performance.

Offline Lyonsio

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Re: The strange green slug like resistor on the early Rd125!
« Reply #4 on: November 21, 2020, 10:47:09 PM »
I was wondering why the RD200 has so many positions on the ignition! I figured it was parking lights or something, kinda like when you turn the steering lock on some bikes and go one position past that the parking light comes on.

Offline Gr8uncleal

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Re: The strange green slug like resistor on the early Rd125!
« Reply #5 on: November 22, 2020, 07:40:42 AM »
My recollection is fuzzy here  :o, but I'm pretty sure that I read somewhere about there being a position for "Emergency Start" (ES). Could be that in the normal position you couldn't kick start it with a flat battery, but in the ES position you could. A bit more research needed to confirm either way, though!
Yam RD200DX (Gr8auntiepat's)
Yam FZX700 Fazer
Yam RD400 bitsa
Yam RD350B rough
Yam RT2 almost finished
Yam DT360A almost finished
Suzi GT550J just started
Suzi 1250 Bandit regular rider
Yam RD125B (probably!) now being reassembled
Yam AS3 in boxes

Offline Astute Greaser

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Re: The strange green slug like resistor on the early Rd125!
« Reply #6 on: November 22, 2020, 01:00:23 PM »
Hi Alan, Lyonslo.
After fitting new tacho to my UK RD200A and swapping old to my USA RD200C (Round tank with front disc) I have an interesting observation.
Alan is correct for the USA black ignition switch there is a ES position.

The II position bypasses the starter relay and allows the generator to start from flat battery with kickstart.

However this is not true of the UK chrome ignition switch. The picture above is wrong. What is a white wire with male bullet on USA connecting into the charge line. Is on the UK a Blue/red with female bullet that connects directly to the blue wire of the headlight pilot bulb.
The UK is not an ES but a day running ablit  lighting only the pilot and tail light not the main/dip beam bulb.
The internal connections of the the two ignition switches are quite different.
The picture is from my Owners manual and caused lots of confusion. Most UK wise, will not realise this (including myself) and will not have used the ES position being fearful of burning out the loom.
Now having said this its up to you to decide what your switches do.
-Mike
« Last Edit: November 22, 2020, 01:03:48 PM by Astute Greaser »

Offline Gr8uncleal

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Re: The strange green slug like resistor on the early Rd125!
« Reply #7 on: November 22, 2020, 01:47:51 PM »
Thanks Mike.

Given Lyonsio's location, I assumed that it was the US switch that he was referring to. However, still lots of room for confusion, given the number of US imports arriving on these shores!
Yam RD200DX (Gr8auntiepat's)
Yam FZX700 Fazer
Yam RD400 bitsa
Yam RD350B rough
Yam RT2 almost finished
Yam DT360A almost finished
Suzi GT550J just started
Suzi 1250 Bandit regular rider
Yam RD125B (probably!) now being reassembled
Yam AS3 in boxes

Offline Astute Greaser

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Re: The strange green slug like resistor on the early Rd125!
« Reply #8 on: November 22, 2020, 02:44:28 PM »
Very true Alan.
More so, the importance that a replacement ignition switch is hooked up correctly for its type/country! Yamaha don't help by only showing the USA wiring  :(. Plus a lot of those imports you mention, are being immediately broken up for spares, as bits worth more than the complete bike   :o >:(
-Mike
« Last Edit: November 22, 2020, 02:50:01 PM by Astute Greaser »

Offline Bluehaze

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Re: The strange green slug like resistor on the early Rd125!
« Reply #9 on: November 23, 2020, 09:36:18 AM »
A resistor would reduce current going through the headlight bulb.
Maybe for daylight use, it's used to increase the light's life while being bright enough to make the bike conspicuous?