does this sound like a short circuit ?

Hi,
The electrics on my bike have completley failed, no ignition, lights or
anything. The battery is fine and so are the fuses. I have a haynes manual
but I'm pretty much a novice at this sort of thing. It states the likely
cause is a frayed wire but as far as I can tell all the wiring looks in good
condition. Can anyone tell me how I should go about finding the fault ?

Any info / help is much appreciated
thanks

 

Bret,
thanks for the quick reply, the haynes states there are only 2 fuses (its a
vespa scooter so there's not much to it) and they are both fine.

 

Get a cheap meter or a 12v test light and start working away from the
battery's positive terminal. Short circuits usually blow fuses or (worst
case) melt down the wiring harness.

 

Won't be a short circuit as such, but an open circuit. Grab your
multimeter and start working back through the wiring. Check all your
ground connections.. they're a common point of failure.

Ben

 

voltage check from battery positive to negative, battery positive to frame,
fusebox to frame.

If OK, check resistance/continuity of both fuses.

If OK, replace fuses and check for voltage at ignition switch.

If you've got any relays in the system, they're also suspect.

If you've got a complete failure of all electrics, it's likely
that you've found it by this point. For a complete failure, my bet
would be something very basic such as a battery lead.

 

The symptoms he describes are "completely failed, no ignition, no lights".

I'd expect it to probably drive the lights OK even if it couldn't
drive the starter. You could also check for this condition by
jumping it from a car battery. If it starts, it's the battery.

 

A lot of digital multimeters can also fool you. They typically have a high
input impedance and don't really load the circuit. This means you can be
downstream of a severely corroded connector, and still see 12.5 to 12.8
volts, but if there was any load, the voltage would drop off drastically.
Sometimes a 1057 bulb with a couple of leads soldered on, or one of the
cheap testers with a bulb is a better tool than a top end Fluke multimeter.

 

Jiggle ......

Battery cables, and leads from battery to starter, etc, gotta be clean
clean. And a little coating of dielectric for good measure, after clean
up.
Just a little "haze" on the cable connecting to Pos side of battery can
make a no start/power situation.


moto

'95 750 Nighthawk (big red)
'95 Helix (little red)
'93 Ninja (up 'n runnin')

 

I know I'm not always going to be smart when I work on a bike.

The best way to compensate for not always being smart is to be
stupid but obsessively methodical. Works pretty well a lot of
those times when that flash of insight fails you.

Enjoy your bike.

 

I agree that your subconscious can solve problems that are
nicely contained. Some problems don't lend themselves to this
though.

One of my favorites was an all night session troubleshooting a
computer problem. At nine the next morning, we still hadn't
found it, an angry mob was forming outside the computer room
and my boss kept sticking his head in the door to say he didn't
think he could hold them off much more.

At this point, I asked again for the umpteenth time whether there
was anything in the test setup that might possibly be different
from the one where the problem occurred. The guy who had been there
when the orginal problem occurred scratched his head and allowed
as how there was one other difference but it couldn't possibly
be signifcant or have caused this problem, and of course that turned
out to be the cause we'd spent all night looking for.

The lesson I got out of all of this was never to rule out things
that "can't possibly" be the cause of a problem. See "Fate is
the Hunter" (the movie).