Only two wires to an instrument with 2 lights?

O

olly

Senior member
So i'm investigating the wiring further on my SF1, the first problem was that the two lighting circuit wires from the ignition were connected to the same pole (number 1) of the ignition switch.

I'm now tracing everything through following the wiring diagram and I'm puzzled.....

The speedo has 2 simple illumination bulbs and a red "beam" light that I think should come on at the same time.  There's an orange "flash" light that the wiring diagram says is a high/main beam indicator.

What's thrown me as there are only two wires going to the speedo and it's all insulated so no obvious further earth anywhere.

Any ideas please?



 
Any ideas please?




Hi
You should have 4 wires from the instrument.
One from flash bulb to connector block 13
One from beam bulb to connector block 20  (The bulb should only be on, when high beam light is on)
One from the 2 instrument light bulbs to connector block 22
One from instrument housing to earth (This do not show on any wire diagrams)

Unscrew the back cover and I guess you would see four bulb holders.
I have four on my SF2.

I would also guess that you have no earth wire on your tacho, and you should have one.

Take a look at this wire diagram for SF1/SF2/SF3. http://www.laverdamania.net/wire3.htm

Regards
 
There's definitely only two going in at the moment and it looks very original and untouched. The tacho cable might be ok as an earth...but the Speedo is a no go surely. The interface between that and the rest of the bike would be via a load of greasy and oily bearings and seals I would have thought. One easy way to check though...I will unscrew it and see
 
The interface between that and the rest of the bike would be via a load of greasy and oily bearings and seals I would have thought.
Click to expand...

At least there is a 100%-connection from the fork to the engine: the clutch cable!
Of course an earth connection from the instrument wouldn't be a disadvantage,
afair there's a cable with an eye simply attached to the housing's bottom side
with a screw.
Ernesto
 
With just two wires you definitely do not have the correct amount of wires.
You need the parking light circuit wire to the backlight globes.
The high beam circuit wire to your beam globe.
Both these earth via the common (green) that connects to the instrument housing behind the chrome cover. From experience it pays to actually run an earth wire to the frame instead of relying on it finding it?s own way back to the battery neg via cables and bearings etc.
The flash globe connects between the plus on the right and the plus on the left blinker circuits so it needs two wires to complete that circuit; The two pole flasher relay has no other option for a flash pilot light.
As H?kon says, all these connections should go through your terminal block.
I just snapped a pic for you to see.
Brown/white is park circuit for backlight
Green is earth
Purple (to orange) and Green (to lt blue) are flash
Blue is high beam
Your tacho will have the park circuit in the same way. However the neutral globe and the gen globe receive a power input from after the ignition switch and these two globes earth via the neutral switch and point 61 (on the regulator DF) respectively. These all also go through the terminal blocks (or what is left of them after 40 years).
See how you go.
Cheers
Lee
 

Attachments

  • Speedo wiring SF.jpg
    Speedo wiring SF.jpg
    70 KB · Views: 24
Right....so it does use the Speedo cable as earth..I will supplement that. My sealed beam. Unit has no parking light. I would prefer  it if the orange flash light was for the indicators only and the red beam is off unless on high beam......hmmm....thanks for hhelp
 
Ernesto said:
Shouldn't the rev counter/speedo cables provide solid and reliable earth connections?
Click to expand...
Ernesto said:
At least there is a 100%-connection from the fork to the engine: the clutch cable!
Of course an earth connection from the instrument wouldn't be a disadvantage,
afair there's a cable with an eye simply attached to the housing's bottom side
with a screw.
Click to expand...

No technician worth his salt would rely on either a speedo/tach drive or a clutch cable for a reliable means of supplying a ground, be it for instruments or illumination.

The instrument illumination may not be vital, but a reliable ground for the headlamp is, headbearings don't count either...

The instruments are mounted in rubber grommets in the bracket, so a seperate ground is necessary for reliable operation, and this should be taken from the frame, not the forks.

piet
 
Right, so I've grounded the speedo to the frame, I'm quite amazed it worked being grounded through a greasy head bearing to be honest.
I probably won't bother with the tacho as that's got a good run to the engine.

My old man's being looking at the wiring a bit more today but I've not had chance to speak to him to see what he's found out.
One "strange" thing about my set up is the sealed beam unit is not supplemented with a dim parking light.  Instead 2 of the 4 wires inside the unit from the bike go to the same terminal on the back of the beam unit (note this is not home a made bit of wire, it's come from a factory like that)
My guess is the intention being that when the side light would have normally being on that the low beam is instead supplied current.

I've looked at the wiring diagram in detail and despite what it says I have decided I want the red "beam" light to indicate high beam only and the orange "flash" light to flash when the indicators do and be off otherwise.  Hope I can get it to do that tomorrow.
 
Is the red jewel for the high beam original? Even though my SF was suppose to have smiths it came to me with ND's and my high beam is blue. Piet is absolutely correct that the ground wire on any circuit needs to be to done with a wire to the grounding point on the frame.

Clay
 
'71 SF said:
Is the red jewel for the high beam original?
Click to expand...

There are no indications the clocks have ever been apart so I'd guess yes, wish it was blue so it's the same as my other bikes and car though.
 
Olly, there have been lots of threads about the different ND instruments that found their way onto Laverdas over the years and yours probably came on the bike. Someone has definitely had a go at your wiring to the instruments though. There is no problem to use your beam lamp (no matter what colour) for high beam only.
None of the SF1-3 range came with sealed beams, all had removable globes and parking lamps incorporated.
If you are not going for rivet counting there are now available plenty of very low amp LED accessory lights that you could mount for park/day-running from the parking light circuit. Alternatively, swap out your sealed unit for a H4 or some high tech modern projector beam or similar, the market has plenty of them. We have the daytime lights on rule here and I have fitted an LED park globe which I run instead of the 55w headlight.
 
You must log in or register to reply here.
Back
Top