Short Circuits troubleshooting

I am trying to track down a problem in a car. A fuse keeps blowing. It is my
understanding one way to do this is to remove the fuse and place a test
buzzer/light in the connections in the fuse spot. With all circuits closed,
I should have no power going through this fuse location. If I have power
there is a short is this correct? I understand power is coming from the
battery to one side of the fuse, but unless there is a "ground" there should
be no power going through it correct? How does that work exactly. Please
keep it as simple as possible. Thanks in advance.

 

"no power"... You mean "power" when the load is connected.

If I have power

If the loads on the circuit branch are disconnected (turned off) and your
test lamp is lit there is a short curcuit. Some circuits can have continuos
loads on them, but would be small and not enough to make the lamp glow. The
resistance of the short or load has to be low or the conductivity high in
proportion to the test lamp for the lamp to glow. If the lamp and shorts
resistance values are 50/50 the lamp will glow at about half it's
brightness. If the short is direct (0 ohms), the lamp will glow at full
brightness.


I understand power is coming from the

The battery is always grounded. The fuse is connected through a buss in the
fuse box to the battery positive terminal through a main fuse.

 

Hi,
Buzzer will buzz until you remove the short or you can use small light
bulb instead of buzzer. Light will go off when short is removed.
Tony

 

Sounds good. Try using a lamp, like a tail lamp where the fuse would be
connected.

Bill

 

The other responders posts are very good suggestions about using a lamp
bulb where the fuse goes to help find the short.

I have a question. Which fuse is blowing? If it is your dash lights that are
out,
I suspect that you just lately installed a radio, tape, or CD player.

ARM

 

car...fuse keeps blowing

If it doesn't make itself obvious, get a Xerox of your car's electrical diagram
out of National Service Data (best diagrams IMO) at your library.

Some stuff is not logical.
Mine has dome lights on the same circuit as radio memory / clock.
(You'd never know it looking at the fuse block.)

 

No actually it is a 20a fuse under the hood in the engine compartment. The
fuse is for Horn, Stop and seat belt retract. It's part of the brake warning
system. Leads to a brake safety warning sensor (light bulb out ect). The
brake lights will not work with the fuse removed. The fuse does not blow
with the left sensor removed, but with the left senor removed, I have no
left brake light.

 

There is a shop manual on line at
http://www.pauldesign.ru/honda/shopmanual.html. The two sensors are
connected in series. Shop manual indicates that there is a diode in one
of the sensors (oftentimes the Honda manuals simplify things by not
showing irrelevant components, there may well be a diode in both, even
though it is not shown). The most common failure mode for diodes is that
they short circuit. If this were to happen in the one sensor you could
get the scenario where you can plug in a bad sensor and the fuse still
would not blow, leading to a false conclusion that the sensor is good.
Assuming the schematic at www.pauldesign.ru is correct for your car, you
would get:

Bad sensor in left socket, good sensor in right socket: Fuse would
blow
* Bad sensor in left socket, right socket empty: Fuse would not blow
Left socket empty, good sensor in right socket: Fuse would not blow

Good sensor in left socket, bad sensor in right socket: Fuse would
blow
Good sensor in left socket, right socket empty: Fuse would not blow
Left socket empty, bad sensor in right socket: Fuse would blow

Page 25-68 of the manual referenced above shows how to test the sensors.
If you get continuity in both directions under point 2, the sensor is
bad.

 

Our library here is small do you think they would have it? Do you think
there is a Library online that may have it?

 

Cracker Jacks

My reference is a bit dated:
http://www.google.com/search?num=100&hl=en&lr=lang_en&ie=UTF-8&oe=UTF-8&q=%22National+Service+Data%22+Mitchell&btnG=Google+Search
especially
http://216.239.57.104/search?q=cache:HRwSNbfOCzMJ:www.lapl.org/guides/automobile_repair.html+%22National+Service+Data%22&hl=en&lr=lang_en&ie=UTF-8
National Service Data is now called Mitchell's
Chilton's, Mitchell's, and Motor's are the Big 3 in independent repair
manuals.
Any library that can truly call itself that should have all 3.
In the big city there are multiple copies of each.

I'm thinking no.