750 ND horn button and handlebar switch

S

smlav

Senior member
Location
Shropshire UK
I’m chasing some electrical gremlins on the SF1 light switch and would appreciate any knowledge. ND switchgear and fitted with separate relays for high, dip and horn. High and low are intermittent, particularly high. With the headlamp bulb removed, the 12V to the bulb connector from the relays is solid when switched on, high and low. If I connect the headlamp bulb, the 12V at bulb connector and relay output stops. Adding the load of the bulb causes something in the loop to stop passing current, my prime suspects being relay contacts or left handlebar switch. So I started by dismantling and cleaning the handlebar switch. This post is about the horn button which has stopped working after rebuilding switch. I'll come back for the light issue if I don't isolate today.

The horn worked solid before I dismantled the switch. It works if I put an earth straight to the relevant wire on the connector inside the switch. The indicator part of the switch has three wires, the black one is a solid earth. I can see that the horn button has a copper post which when the button is pressed strikes a contact opposite the horn wire, and that should earth and activate the relay/horn. But where does that copper post on the button get its earth from? Is it somehow from the black earth wire at the indicator part of the switch? Or is it from the switch body, which doesn't appear to be earthed (with switch off the bars) - should it be?

Thanks. Sean.
switch-1.gifswitch-2.gif
 
Don't know, I am guessing through the switch body to the handlebars to the frame, rubber bar mounts wouldn't help. My first ever mod and failure came from getting sick of being almost run over, so I added dual Framme horns to mt RD 250 and promptly melted the horn button spring. Relays were a mystery to me in 1975.
 
The wiring in your switches is no longer standard, wrong shades/colours, possibly also wrong colours connected to wrong terminals.

The indicator switch should not have an earth connection. +12V coming from the relay in the centre, the other 2 wires distribute the supply to LH and RH indicators. The bulbs themselves (should) have the necessary earth.

The alloy switch body has an earth connection (black/white), this was rarely used on Lavs. The wire is often fitted to the switch but not connected at the other end. If it is missing, you should find an unoccupied M3 thread in the alloy body. Always a good idea to have that connected, otherwise you're relying solely on the head bearings and operating cables (clutch, choke, throttle, etc.) for an earth connection! The horn switch should have +12V coming from the horn, the button grounds the 12V, completing the circuit. With the wiring degrading over the decades, it's advisable to operate the horn through a relay, especially if twin horns are used. When testing with the switch blocks apart, use a test wire and alligator clips for a good earth to frame or engine.

Using a wiring diagram can only help to determine what connects where. If the loom and wiring have been altered/bodged in any way, the connections at the various switches must first be checked, that's where patience, common sense and a little understanding of electric principles kick in.

piet
 
Thanks both,
I think the switch is actually from a Suzuki fitted by one of the previous owners; it's old wherever it came from and benefited from a thorough clean internally. The wiring is tidy, said to have been installed by S.Winterton some time ago. That indicator switch has earth at end connector, and the other two go to the relay for left and right flashers, they work well so am not messing with them.

I earthed the switch body by putting it against frame and horn works. So that button gets it's earth through the switch body and through the bars. It's on a relay, so small current only and I'm not worried about it now I've established the current flow.

There's no B&W wire in this switch. I think, but will be checking shortly, the main and dip beams get 12V in and the switch sends the 12V to the relevant relay coil. And I'm hoping that when under any load the relay is failing to maintain its contacts. Ideally it would be simple swap out relays, but my replacements have pins in different layout so will have to mess around a bit.

I really hope it's relays rather than the switch. I have a pattern switch from a Suzuki GS550, but that's completely different wiring and will be a bigger job to swap out than the relays. Best left for winter.

Sean
 
Period Suzuki switches have identical wiring to that used on Laverdas. I actually had a OE Suzuki switch on my 3C for years, wire colours tallied with Lav diagrams.

That indicator switch has earth at end connector, and the other two go to the relay for left and right flashers, they work well so am not messing with them. Arse over tits to how it's normally done. :ROFLMAO:

piet
 
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I don't think it's possible for that black wire to be an indicator earth - if you look at the way the thumb knob operates inside you'll see that it simply connects the middle (power) to either left or right via a copper slide connecting brass contacts. My guess is you're confusing the black as an earth because of the colour.

Headlight issues sound like simply relay failures. Piss easy to check by swapping Low and High relays or just fitting the unused one you have. They basically all use the same number codes (30 from batt+, 87 to headlight, 85 and 86 handlebar switch or earth) - it doesn't really matter if you reverse 85 and 86.
 
I checked the black wire with a meter, definitely earth. The other two wires each flash 12v when an indicator is on, one does left and other does right. I think as Piet said, this switch is not same as standard Lav switch.

Headlamp issue confirmed as relays, the thing which threw me is that both the high and low beam relays suffering the same failure which made me suspect the switch. I guess the relays are the same batch/age and if they've sat a bit they have suffered similar degradation on the contacts. The high beam was very if'y, the low beam worked most of the time. If the bulb didn't light, flicking the relay a few times would bring it on. Swapping the relays over and the very if'y tracked the relay, ie. low became the worst.

It's 30 and 86 which are different on the relays I bought yesterday, so they don't just pop into the relay holder socket - well they do, but with pins 30 and 86 are swapped. Easy sorted now I know where the smoke is escaping.

thanks
Sean
 
Out of curiosity I asked Chatgpt about ghe wiring for left hand switch. It pointed me at a few wiring diagrams, and gave the below. Identifies the issues discussed here re horn button.

Unfortunately, I wasn't able to find an explicit textual list of wire colors specific to the left-hand handlebar switch on a 1973 Laverda 750 SF1. However, I did find reliable insights from knowledgeable forum contributors regarding typical wiring.

What the Experts Say

A useful discussion from LaverdaForum sheds light on the wiring configuration:

  • Orange – power feed into the left‑hand (LH) switch from the fuse box
  • White and Yellow – high and low beam outputs from the switch to the headlamp
  • Grey – park/tail light circuit, active in both "park" and "on" switch positions
  • Blue (from flasher relay), Black, and Light Green – related to the indicator controls for left and right signals
  • Dark Green – horn circuit, earths out via the horn button
  • Black/White – chassis earth connection for the switch housing (often not shown in factory diagrams but used for earthing, especially on rubber-mounted handlebars)
 
smlav said:
Out of curiosity I asked Chatgpt about ghe wiring for left hand switch. It pointed me at a few wiring diagrams, and gave the below. Identifies the issues discussed here re horn button.

Unfortunately, I wasn't able to find an explicit textual list of wire colors specific to the left-hand handlebar switch on a 1973 Laverda 750 SF1. However, I did find reliable insights from knowledgeable forum contributors regarding typical wiring.

What the Experts Say

A useful discussion from LaverdaForum sheds light on the wiring configuration:

  • Orange – power feed into the left‑hand (LH) switch from the fuse box
  • White and Yellow – high and low beam outputs from the switch to the headlamp
  • Grey – park/tail light circuit, active in both "park" and "on" switch positions
  • Blue (from flasher relay), Black, and Light Green – related to the indicator controls for left and right signals
  • Dark Green – horn circuit, earths out via the horn button
  • Black/White – chassis earth connection for the switch housing (often not shown in factory diagrams but used for earthing, especially on rubber-mounted handlebars)
Click to expand...
'73 SF1 would have Lucas switches, same as late Triumph, BSA and early Norton Commandos. The connections for these are shown in the corresponding Laverda wiring diagrams, see Green Book. The above colours are correct for the ND switch bodies. Light blue and light green supply left and right indicators.

ND switchgear was introduced with SF2 and 1974 triple.

piet
 
Drum brakes front and rear, engine and frame 14005, engine stamped SF1. Lavmania register has it as '73 SF1. The records I have show it coming to UK around 2004. Electrics very much altered since then, single coil, electronic ignition, non standard (but still mechanical) regulator, relays for everything, very neatly done - none of the spaghetti in the headlamp like my GTL. ND switchgear, ND clocks and the mounting bracket is same or similar as my GTL, Bosch H4 headlamp - 160mm, smaller than the 180mm on my GTL.

I only put the chatgpt thing up for curiosity, I think it just trawls the www and one of it's main sources of info was this forum. Quicker than searching, it did tell me about the horn button earthing. I rebuilt the switch last night and put it back on bars, horns work good now. I also ordered three new relays (1 spare) with same pin config as the failed ones. Once fitted, I'll be taking the sealed failed one apart to see if it is indeed corroded contacts.

I'm in process of getting to know the bike so that when I ride it to Spain for the Colombres rally later this year I know which tools and spares to carry, and I'll be able to identify (and hopefully deal with) any issues which arise. Am expecting about 2k miles round trip.
 
smlav said:
Drum brakes front and rear, engine and frame 14005, engine stamped SF1. Lavmania register has it as '73 SF1. The records I have show it coming to UK around 2004. Electrics very much altered since then, single coil, electronic ignition, non standard (but still mechanical) regulator, relays for everything, very neatly done - none of the spaghetti in the headlamp like my GTL. ND switchgear, ND clocks and the mounting bracket is same or similar as my GTL, Bosch H4 headlamp - 160mm, smaller than the 180mm on my GTL.

I only put the chatgpt thing up for curiosity, I think it just trawls the www and one of it's main sources of info was this forum. Quicker than searching, it did tell me about the horn button earthing. I rebuilt the switch last night and put it back on bars, horns work good now. I also ordered three new relays (1 spare) with same pin config as the failed ones. Once fitted, I'll be taking the sealed failed one apart to see if it is indeed corroded contacts.

I'm in process of getting to know the bike so that when I ride it to Spain for the Colombres rally later this year I know which tools and spares to carry, and I'll be able to identify (and hopefully deal with) any issues which arise. Am expecting about 2k miles round trip.
Click to expand...
It started life as an SF1, 1973 model year.
Was originally Lucas switchgear.
There wouldn't have been spaghetti in the original thin CEV chrome plastic headlight, no room for it.. The 160mm Bosch is SF2/3. It would have been in a spaghetti box forward on the frame. There's very little wiring in the headlights of the SF2/3.
Paul
 
Thanks Paul,
It’s metal shell headlamp now with zero wires or connectors other than headlights. I guess someone must have gotten access to parts from an SF2 - would have been expensive to get so many parts new. The relays are all tucked behind headstock, tight but neat.
Sean
 
the connector blocks (terminal bank) under the tank, right hands side ,differs between the SF1 and SF2, they are not the same and do not have the same number of "ways".
It does very much sound like the wiring that Stevio was doing 20 and 30 years ago, he can still be contacted and might be your best choice for rectification, although the warranty will have expired long ago (not that he ever gave one anyway). I do not have his contact detals, but someone on here will no doubt provide.
CLEM
Piet, I beg to differ (my VERY learned and much trusted friend) but when I owned an unaltered (bought new by me) SF1, I had a need for Lucas switches and I found that the type for Brit bikes was wired differently, OK if you can repair watches and use a small soldering iron, since (IIRC) one wire in each switch has to be unsoldered and attatched to an unused lug, to provide normally open to normally closed switch, or the other way around, do-able yes, but not that easy for mechanics that can get spark plugs cross threaded, and think that carb balancing involves weighing them.
CLEM
 
Thanks Clem, but I don’t need anyone to look at it, it’s just swapping out some relays. I want/need to have a handle on things so that if it dies on me in some remote location stand a chance of getting it going again. The regulator and ignition are the bits which could be a problem. I’ll be okay to just carry a modern digital regulator, but the electronic ignition is not one of the common ones. I’ll just hope it lasts the summer out, and come winter I’ll investigate the practicalities of carrying a spare for longer trips.
Sean
 
smlav said:
Thanks Clem, but I don’t need anyone to look at it, it’s just swapping out some relays. I want/need to have a handle on things so that if it dies on me in some remote location stand a chance of getting it going again. The regulator and ignition are the bits which could be a problem. I’ll be okay to just carry a modern digital regulator, but the electronic ignition is not one of the common ones. I’ll just hope it lasts the summer out, and come winter I’ll investigate the practicalities of carrying a spare for longer trips.
Sean
Click to expand...
Which ignition is it using?
Paul
 
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