I have a 1936 model 16H that has recently started to blow the fuse just off the battery each time I take her for a ride? Whilst stationary and ticking over the fuse is okay, even after trying the front lights, rear brake light and horn, but blows when I’m out riding? This is happening now each time I go for a ride. I’ve not changed anything electrical on the bike as of late, so was wondering if anyone may have an idea what may be causing this issue please?
... for a wire trapped somewhere that's making contact with the frame when under way - perhaps where it passes under the tank / in front of the seat? Or when the seat springs are compressed making contact somewhere it shouldn't.
Does it happen if the lights are off - in which case it must be in the main battery lead.
Replace the fuse with a bulb, bulb will glow in line with the current flow so when its at its brightest you have the short and can try and track it down.
Yes but replacing the fuse with a lamp is fine when stationary but zooming (trendy word) down the road could be awkward! As the bike runs on the magneto then there is no real need for battery power. SO if you remove the battery power that feeds to the ammeter (make the wire safe wrap in tape etc) then go down the road again, does it blow the fuse? A good place to try is the stop light (if you have one they were optional before the 1950s) as this usually has live battery power fed to it. As 2 posts above note any places that jump about when going down the road and look closely for the frayed wire and shiny metal work it is shorting to.
If so , what rating and what is it protecting. You say it’s not a switchable load that’s causing the failure so it’s brake light circuit or the distribution wiring. Do you have accessories like horn or indicators fitted ???? Is the fuse the correct rating? Follow as Al suggests... there will be evidence somewhere...
Thanks for all the comments, I’ll have a look at the wiring to start with then, to see if there are any worn areas earthing back?
FYI - It’s the 35amp fuse in a fuse holder on the live wire, just after leaving the battery housing. I ride without lights on, other than the rear brake light when I’m braking. All works when I leave, however fuse is blown when I get back home.
Thanks again, I’ll investigate!!
My 16h would blow the (non-standard) fuse too. I fixed it yesterday; on mine it turned out to be the horn/dip switch unit.
Don't know the make, but has a round metal horn push and black plastic switch. The fault was traced to the casing of the switch being too close to one of the brass contacts within the switch. I simply filed down the brass contacts to ensure they couldn’t touch the casing.
Ive now fitted a 5a fuse and it’s fine, which surprises me as I tested it with lights on and horn activation.