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fuse blows when probing the wire


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rock1 
Copper - Posts: 120
Copper spacespace
Joined: April 06, 2005
Posted: April 06, 2005 at 11:46 AM / IP Logged  
why would a fuse blow when probing the wire.
Optik 
Copper - Posts: 53
Copper spacespace
Joined: March 16, 2005
Location: United States
Posted: April 06, 2005 at 11:54 AM / IP Logged  
hmmm lets think about this question...... bad connection, you probed too deep and grounded connection, probed into another connection. Maybe your probe is broke.
thepencil 
Gold - Posts: 1,526
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Joined: December 16, 2002
Location: Canada
Posted: April 06, 2005 at 12:21 PM / IP Logged  
You better know what you are probing. Better be safe than sorry, use a digital mulitimeter. Use this piece of equipment and it will answer your question WHY.
Be careful whose advice you buy, but be patient with those who supply it.fuse blows when probing the wire -- posted image.
rock1 
Copper - Posts: 120
Copper spacespace
Joined: April 06, 2005
Posted: April 06, 2005 at 12:27 PM / IP Logged  
the wire was the main wire for the trunk and gas
so the probe light is not safe? If you have to probe wires to install an alarm how can you if you dont know what wire is what in the car. the alarm manual says probe the wire or wires and find a wire that shows a 12v+. you have to probe by trial and error.
geepherder 
Platinum - Posts: 3,668
Platinum spaceThis member consistently provides reliable informationspace
Joined: October 27, 2003
Posted: April 06, 2005 at 2:03 PM / IP Logged  

A simple test light should not be used to probe wires.  It does not offer much resistance, and can draw much more current through a circuit, frying computers and the like.  Use a multimeter, or a logic probe. 

My ex once told me I have a perfect face for radio.
rock1 
Copper - Posts: 120
Copper spacespace
Joined: April 06, 2005
Posted: April 06, 2005 at 2:59 PM / IP Logged  
the probe light came with the car alarm in the box and the manual says to probe the wire or wires that must mean to test any wire.
how does the multimeter is it safer then the probe light?
thepencil 
Gold - Posts: 1,526
Gold spacespace
Joined: December 16, 2002
Location: Canada
Posted: April 06, 2005 at 3:20 PM / IP Logged  
Read through here and you will understand why.
Be careful whose advice you buy, but be patient with those who supply it.fuse blows when probing the wire -- posted image.
rock1 
Copper - Posts: 120
Copper spacespace
Joined: April 06, 2005
Posted: April 06, 2005 at 3:47 PM / IP Logged  
so the DMM works the same as a probe light but does not send out current to the wire and blow a fuse?
geepherder 
Platinum - Posts: 3,668
Platinum spaceThis member consistently provides reliable informationspace
Joined: October 27, 2003
Posted: April 06, 2005 at 4:04 PM / IP Logged  

When you're testing for voltage, you're actually creating a parallel circuit with the equipment you're checking.  Think about it.  Now both the gear you're testing, and the light have to draw power.  When you create a parallel circuit, your total resistance decreases- plain and simple.  As resistance decreases, current increases, and your fuse blows. 

Now most multimeters (and logic probes) have internal resistances into the Mohms (millions), so the decrease in total resistance and increase in total current is negligible.  However, if you put a test light in the equation, which has maybe- 20 ohms (just picking a number), it will have a much greater effect on the operation of the applicable circuit.

My ex once told me I have a perfect face for radio.
rock1 
Copper - Posts: 120
Copper spacespace
Joined: April 06, 2005
Posted: April 06, 2005 at 4:18 PM / IP Logged  
im trying to test for the door locks for the alarm
the unlock wire is in black plug in kick panel and there is more then one black wire there I dont want to blow a fuse with the probe light so I will try the dmm.
How can I use the DMM to find the unlock wire if I unlock the door I would see the DMM change?
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