Thought I’d ask on here before I start tearing everything apart just in case…
Headlight blows and idiot lights stop working apart from the “light on” idiot light - the pilot light is on.
New headlight bulb, everything works perfectly.
After a while the headlight blew again and idiot lights stopped working.
The rear light, brake light and horn work, no indicators on bike. Bike runs perfectly.
New headlight bulb but this time didn’t fix it.
This is where one of you says “oh yeah, common problem: that’s the yellow strand of spaghetti that needs properly connecting to the ravioli with a bit of grappa - easy!”
Or, “Nah mate, take it to a specialist”
I hate electrics
Try taking the fuses out and cleaning the ends of the fuses and the holders, also disconnect any earth wires from the frame and clean the terminal and the frame where it bolts on. Those are usual cures for bad circuit connections but it sounds like you have a fuse that keeps blowing, maybe a crossed wire in the headlamp shell?
And, most likely cause and quickest way of blowing a filamant bulb is an intermittent connection (guess how I know) … Wiring harness will be 40+ years old, unless it’s been rewired since … so I’d be looking for loose or crusty or oily or dirty connectors … I’m pretty sure all the ‘idiot’ lights are powered from ignition circuit (Fuse #1?), except the lights-on indicator and turn signals, so in this case seems that is getting 12V (when lights are on) and the others aren’t. Apart from fuses also consider ignition switch, 4 bullet connectors in the base I think, which can be loose / corroded / falling out, I have even heard of the switch coming apart.
The pilot light, tail light, instrument lights and lights on indicator are on a separate fuse as they also do the parking light function.
First thought would be an earthing fault, possibly from the headlight itself, but what is causing the headlight bulb to blow? There could be a frayed wire somewhere that is intermittently shorting out.
Have you done anything t the bike recently, like taken the tank off that could have pulled or trapped a wire.
I have heard of shorts occuring within the lego switchgear onto the handlebars, worth popping the left switch off to look for any bare wire that could touch the bars.
Put the key in, turned it on and everything fine!
Went through all suggestions received as not convinced it had fixed itself and still seems to be working ok.
So 40 year old wiring still works, who said Italian electrics wee rubbish?
My first ever Guzzi was a T3 bought back in nineteen oatcake super cheap because it wasn’t charging. Took about 10 minutes to to clean earth contacts and every thing was perfect. NHW 732R if anyone on here has it, it’s taxed so still being used, probably with the same electrics??
I think perhaps your headlight bulbs didn’t actually blow, I assume you didn’t check them with a meter before you threw them away. The T3 has those torpedo shaped fuses. They are susceptible to wearing through/corroding where they fit in the holder. Replace them with new ones but if you get stuck away from home you can usually rotate them 180 degrees and get home.