I switched off the motorcycle and it wouldn’t start again. Turns over fine, but no spark at the plugs. I don’t have the relevant wiring diagram and frankly am all at sea when it comes to electrics. Any advice on where to start would be much appreciated!
kill switch?
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Kill switch would be the place to start. Continuity test across it to make sure it’s switching.
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Kill switch first suspect. You may find it easier to undo the fuel tank and find 3-pin block leading to it, and try there, without opening the switch itself, as this can be tricky with undoing carb cables etc. Of three wires, two are white, and if you bridge them, you effectively do the killswitch job.
Thanks, Steve, Barry and Adamigo! It sounds unanimous - I’ll have a look at the kill switch this morning.
Some of the police spec bikes came with a sidestand switch I believe - if fitted this energises a relay that powers the Ignition system. May or may not be fitted but a fault would cause no sparks.
Russell
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Now that is a good shout.
FWIW. I stood there for a full eternity once cursing and check-check-rechecking everything before I reluctantly admitted to myself that Yes, the keys are in the ignition but not turned to Go.
Keep us updated? If nothing else, it helps future readers who might come in search of a solution to a similar problem.
I was on a extended trip with friends and a Suzuki belonging to one of the group wouldnt start in the rain - ended up with the tank off wires disconnected, WD40 on everything, much scratching of heads - turned out the kill switch was in the off position 
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More times than any of us would care to admit?
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I pushed a bike home once over a mile because it wouldnt start after I jumped off at a shop in a hurry.
next day I went out to fix it, and found i had accidentally hit the switch when I jumped off 
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Thanks for your suggestions, everyone. I have done the whole “draining the battery with the kill switch off myself, but alas not this time. I isolated the kill switch, which was working. I took it off and gave it a good clean, to be on the safe side. Still working when I refitted it. I also bridged the sidestand switch, but there are still no sparks either side. Where next, please?
Is this a points ignition or electronic ignition bike (probably electronic) but checking first. Can you see if it a Bosch or Rita system (Bosch has two igniter boxes the Rita has one)
Do you have a multimeter available ?
What year is the bike (1992 ?)
Russell
The plate says ANNO 1991 and also ANNO DI CONSTRUZ. 1992… It’s a Bosch system. I have a multimeter somewhere.
Check all the fuses are tight in the board - these old fuse boards can loosen their grip on the fuse as the brass clips age and open up -A rubber band around each fuse and its clip is a quick way to resolve this issue and ensure the tip of the fuse is making good contact with the fuse retainer clip. My V 50 Monza of old was guilty of this
Good tip. For general maintenance if not for this specific fault. A bit of emery in one hand, and a mug of tea in the other. Sunday morning job, time well spent.
On one of the Tontis I had, the push on terminal clips to the coils was a favourite to come adrift. It was that bike’s Thing. You get to know, right?
ahh memories - mine was a pain in the ass - it would only do it when the bike was hot and running then behave when cold… I do recall swearing profusely at it and doing a “Basil Faulty” beating it in frustration before I twigged…..intermittent electrical faults are the devils work.
Italian electrics were basically rubbish in this period…… they don’t ever get better with age
Check the fuses as per the previous post - Im not sure that they are in the Ignition circuit but it cant hurt. The old eurofuse boxes are notoriously flakey as they dont hold the fuses very tight and are susceptble to corrosion.
First check with multimeter
Ignition on, side stand up, tank off, set multimeter to volts and check from the red wires in the feed to the igniter boxes to earth - you should get around 12V. Likewise test on the red coil feed wires to earth, again you should get around 12V - if either of these tests show 0V or low voltage you have a power supply issue.
Let me know
Also makes sure all the connections to the Igniter boxes and Ignition pickups are clean and tight.
Russell
Thanks everyone for your replies. I went through the wiring which was mostly showing no current, and cleaned every terminal. I now have sparks on both sides and have fired the engine up. It is now racing like mad so I suspect that the throttle links are trapped or dislodged, so it’s off with the tank again today and try to rectify this. Still, it’s progress…
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appreciate the update. it helps future readers, i think, to see “this worked”.
trapped throttle cables? someone showed me to loosely tie them in position with a length of twine. emphasis on loosely - cable ties can restrain them too tightly. just keeps things where they should be as you fight with the tank 
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I had trapped the throttle cable in the twistgrip while reassembling it, following checking and cleaning the “killswitch”. All working well now, thanks everyone.
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