Blowing Tail Light Fuse

[Goosed Again]

Well, it's not at the tail light assembly, I disconnected that, replace the fuse, turned the ignition key, and POP goes another 5 amp weasel. Anybody got any good recommendations on where to check next?

[Kiwi_Roy]

The tail light fuse also feeds the park lamp in the headlight and the lamps in the speedo and tach.

 

A trick I use for an intermittent short is replace the fuse with an old headlamp bulb, with no short the lamp is out, Wiggle the wiring and create a short and the lamp flashes.

[Goosed Again]

"replace the fuse with an old headlamp bulb" I'm not quite understanding you on that one. I'll open the headlight housing tomorrow and take a look there.

 

Thanks

[JBBenson]

I had the same issue, turned out the tach bulb socket had broken loose and was shorting against the metal tach housing......I ended up epoxying it back in.

[Kiwi_Roy]

"replace the fuse with an old headlamp bulb" I'm not quite understanding you on that one. I'll open the headlight housing tomorrow and take a look there.

 

Thanks

If you get a short circuit you might blow many fuses before you find the cause.

If you take one of the blown fuses and connect it to a headlight bulb then plug it into the tail light fuse holder.

 

If there is a short the headlight bulb will shine brightly

If there is no short the lamps will work as normal, the headlight can provide 2-3 Amps.

If you have an intermittent short the headlight bulb will flash every time you wiggle the wires, no fuses will be harmed in the process.

 

The headlamp acts as a current limiter, it will supply about 2 amps into a load, more than enough for most small loads before it starts to heat up, double that if you wire up both filaments in parallel

While the lamp is cold it's resistance is quite low, but if there's a short to ground downstream the filament heats up and the resistance goes sky high.

Magic resistors I call them.

With the current limited this way there is no possibility of doing any damage, unlike the 500 amps you might get from shorting out the battery. 

[Goosed Again]

Still baffled, no offense Kiwi_Roy, I still haven't tried the headlamp hook up yet cause it makes no sense (the physical act) to me. And I'm really not electrically inclined.

 

I jiggled wires, cleaned and reseated relays, cleaned terminals. Pulled the starter and checked/cleaned terminals, cleaned and reseated bullet connections where i could find them. I don't see any exposed wires, is there anything I'm missing?

 

Anyone have any other ideas?

 

Again, this isn't when I hit the starter button, this is when I first turn the key the 5 amp fuse for the rear tail light. The brake light works fine, headlight's fine, turn signal work, bike starts and runs. I've disconnected the tail light assembly and the fuse still pops.  

[Gio]

+1 on the lamps on speedo or tach being the likely culprit ... notoriously dodgy and did away with 'em many years ago.

[stewgnu]

+2

[Goosed Again]

The  +1 and + 2 on the instruments got me taking another look and sure enough, it was the lamp socket on the speedo side. I had taken off the tach before but the speedo was holding tight so I didn't bother. This time I attacked it more aggressively, prying little by little with a flathead and sure enough it came out and exposed the culprit - the busted lamp assembly. That's the good news, I even put in a new fuse with the lamp disconnected, turned the key and no POP! 

 

The bad news is that when the speedo came out I heard something fall into the bike. It's that little brown wafer at the bottom of the socket I guess, everything else seems to be there. I looked around... nothing. Took out my compressor and gently blew around trying to scare it out... nothing. We have a Ducati dealer in town, sure hope they have that lamp assembly and it's a painless purchase.

 

Thanks all!

[Gio]

Glad you found the problem Goosed. Not sure if I would replace with the same items (as likely same will happen again) - others have gone alternate routes (LED?) ... I just do without them.

[docc]

Some of us have epoxied them permanently with JB Weld or the likes.