Ok .... trip to Halfords and bought up most of their stock of 20A fuses! :)

It seems that the LED stop light is the culprit - but ONLY if the engine happens to be running at the time. I can use either of the switches when engine is not running and the stop light functions fine. If the engine is running however, then either switch will blow the fuse first time the light operates (it does flash for a second then the fuse pops).

Half a dozen fuses down and my prognosis then is that there is something that doesn't like being vibrated in the rear light unit, so I will strip that down and check it.

Thanks for your advice, it helps to focus rather than the reaction of "oh my god that tends to overwhelm me when anything happens like this". ;)

No worries.

Usual culprits when things like this happen are recent changes - in this case the LED unit.

It sounds like it has a bad LED in there somewhere, which is breaking down under the higher voltage supplied when the bike is running (and charging), rather than with the lower voltage of just the battery.

You should send it back and get a replacement as it's obviously not right.

I have just tried it with the LED unit hanging out and all the wires stretched out and it seems fine now. All I have to do is ride with the guts of the tailight hanging down pointing at the ground and it'll be fine! :)

Seriously though, it looks like there is a bullet connector in there that is not very well shrouded and it must be almost touching one of the exposed terminals on the light so the vibration does the rest. The Casoli light unit I have plugs into the original light fitting so there was no rewiring to do, but there is not much room in there.

More likely, the problem developed last year when I fitted the number plate tidy because that required a rewire of the plate light. I was obviously a bit careless in my routing of the wiring.

[Edited on 4-5-2005 by HW]

Glad you got it sorted before the trackday on Monday. See ya there!

That was on my mind too ... I would have taken a pocket full of spare fuses! Once it started it was OK, because that was the only thing (plus the stop light) that it really affected. Can't beleive I rode in the rain and fog last night to meet the Lincs lads for a drink with no stoplight! :puzzled:

Really? Cool. Do tell .... :puzzled:

Urghhhh .... Yesterday I reported that it was all working with the tail light innards hanging out, and I (wrongly) assumed that the problem was inside the tail light. I have reassembled it all this morning with tape around the connections inside the housing ... and found that when back on the bike it still blew the 10A fuse when you operate the stop light with the engine running.

I think I have now solved the problem though.

A few more blown fuses and I am pretty sure it is the wires where they come out of the metal tube under the exhaust. The fuse only blows when I do up the 2 back screws tight. Whilst I cannot actually see a break in the insulation where the wires go into the plug, I have wrapped gaffer tape around the exposed wires and pushed it back into the tube. Now when I tighten the screws on the light unit and test it does not blow.

Tonight will be the "acid test" because I am doing a 50 miles round trip.

Picture of how the wires look where they come out of the tube. The light unit screws up on either side at this point so I think it was pressing the wires against the sharp edge of the tube.

Henry, a tip to save on fuses when you are troubleshooting a fault. Get a 21W indicator bulb and solder a couple of wires on to it with bare ends. Jam the ends into the fuse holder so that the bulb replaces the fuse.
When the short is there the bulb will glow at full brightness, when the short isn't there it will glow dimly or not at all depending on the load drawn.
This can save you a lot of money at Halfords who must sell the most expensive fuses in the country :)

Ah ... good thinking that man! Halfords are pretty expensive (£1-15 for 3) but in Grantham it is pretty well all we have available. If the problem presists I will construct something for that.