Dead Short

Joined
Feb 5, 2018
Messages
257
Location
So. Cal
Easiest way to find a dead short without test equipment? keep blowing turn signal fuse (92 Nissan Pathfinder) sometimes the fuse will last a few months sometimes it blows w/in 15 minutes. must be a loose wire shorting out. just cant seem to find it.
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yes. and I should also note that the emergency flashers work and they use the same bulb (not sure if they use the complete same wire circuit) I was thinking since the flashers work but the turn signal blows the fuse it might be in the turn signal lever?
 
The easiest way to find a short without test equipment is to buy test equipment. That's like asking what's the easiest way to ride a bike without a bike.

I mean sure, you can look for broken wires, black scorch marks, molten areas, sparks, smoke, fire, and little ninjas with wire cutting swords, but otherwise you are going to have to check on whether the emergency flasher does use the same wire ( pull the bulb housing and see if there's more than one bulb element or wire involved), and if it does you could always run a new wire. If it doesn't use a different wire then yes it is probably your signal lever which may or may not lend itself to being opened, inspected, and possibly cleaned out. Depends on how much trouble that is, whether to take it out to check it and possibly clean it, rather than buy a new one ahead of time.

If you have any kind of bulb out alert system in the vehicle, that monitors the flashers, you might also use your unavailable test equipment to check that too.
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A multimeter is well worth owning, even if it's a low end $10 special.
 
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i'm not electrically inclined. what specific test equipment can find a short? I have used a multi-meter to test batteries
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but that's about it
 
It's not a "dead short" if it occurs intermittently. Testing when it isn't shorted (which is almost all the time) will not reveal anything. Though of course you should look for frayed wires, broken parts and other obvious potential problems.

And you say the hazards don't cause it, but you only turn them on for a brief test.

First note if it happens on right or left turns.

There are circuit breakers that plug in in place of fuses, swapping in one of those can help reveal the problem since it will reset and let you try again.
 
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This is a joke, sort of. Replace fuse with solid wire, carry wire cutters. When you smell rubber burning, hunt for the melting wire and cut it in two. Where the melting stops, there is your short.

Please please do not do this. I did know an old time mechanic from the 50's that would use this method. Of course cars then had like 20 wires total.

Rod
 
You can also do the wiggle test to find an intermittent short if the fuse isn't blowing immediately. Put in a new fuse and start wiggling wires. When they fuse blows many times you found where or close to where the short was.
 
I believe that the hazards are on a different circuit/fuse and I believe that the turn signal fuse also powers the backup lamps.
Does your Pathfinder happen to have a trailer wiring harness? If so, trace the wires down and look for a frayed wire. Also, if it has a logic box (very likely), it could be the source of your problem. The easiest way to check this is by disconnecting it from the vehicle to see if the fuse stops blowing.
This is the correct tool to use to find automotive electrical short circuits.
https://www.amazon.com/Tool-Aid-25100-Short-Tester/dp/B000RFLR0U
I have had one in my tool box for many years and have used it many times to find shorts.
 
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Originally Posted by Dave9
The easiest way to find a short without test equipment is to buy test equipment get a wiring diagram. That's like asking what's the easiest way to ride a bike without a bike.

I mean sure, you can look for broken wires, black scorch marks, molten areas, sparks, smoke, fire, and little ninjas with wire cutting swords, but otherwise you are going to have to check on whether the emergency flasher does use the same wire ( pull the bulb housing and see if there's more than one bulb element or wire involved), and if it does you could always run a new wire. If it doesn't use a different wire then yes it is probably your signal lever which may or may not lend itself to being opened, inspected, and possibly cleaned out. Depends on how much trouble that is, whether to take it out to check it and possibly clean it, rather than buy a new one ahead of time.

If you have any kind of bulb out alert system in the vehicle, that monitors the flashers, you might also use your unavailable test equipment to check that too.
wink.gif


A multimeter is well worth owning, even if it's a low end $10 special.


Fixed it for you. Any time you have an electrical problem, your very first step should always be to get a wiring diagram. How are you going to trace the wires from one end to the other if you don't know where they go and what they connect to? How do you know which wires should have voltage if you don't even know how the circuit works? A wiring diagram lays it all out and shows you exactly how the circuit works, where the wires go, the color of every wire, any connectors and splices they go through, including which pin in the connector they're connected to, the location of the connectors and splices, and some even show the route/location of the whole wiring harness.

Trying to solve electrical problems without a wiring diagram is like trying to fix it while blindfolded.
 
i cleaned the battery terminals but did not check condition of the battery cable. if the negative cable was bad, wouldn't it blow more fuses than just the turn signals?
does not appear to have a trailer wire harness
 
A dead short will always blow the fuse immediately. You have a loose bare wire, contamination across terminals or a loose connection near the fuse.

A voltmeter is cheap. get one and Put it on appropriate Amps measurement then measure across the blown fuse with the circuit hot. Is the amp draw close to value of the fuse? If so over time it will blow. If not Is it the correct fuse value and is it a Chinese fuse from harbor freight? Check the bulb socket for contamination (partial short). Make sure the connections the fuse plugs in are also clean. Loose connections will generate heat which can conduct up to the fuse filament and melt it.
 
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Originally Posted by ragtoplvr
This is a joke, sort of. Replace fuse with solid wire, carry wire cutters. When you smell rubber burning, hunt for the melting wire and cut it in two. Where the melting stops, there is your short.

Please please do not do this. I did know an old time mechanic from the 50's that would use this method. Of course cars then had like 20 wires total.

Rod

We always called this the "NO-BLOW" fuse-if it burst into flames, you fixed it (call 911!)! Seriously, does it happen in the rain, or on bumpy roads? Might be as simple as a shorted socket or a wiring harness rubbing on something.
 
based on the responses, dead short is not the correct term as the issue is intermittent so it must be a loose wire or a wire with worn insulation touching against metal. First I thought it might be water causing a wire to short as it occurred soon after a recent rain however it has been dry here for several weeks so I don't think that is the issue. I'm still searching for a wiring diagram. surprisingly hard to find one!
 
Originally Posted by VQLT
based on the responses, dead short is not the correct term as the issue is intermittent so it must be a loose wire or a wire with worn insulation touching against metal. First I thought it might be water causing a wire to short as it occurred soon after a recent rain however it has been dry here for several weeks so I don't think that is the issue. I'm still searching for a wiring diagram. surprisingly hard to find one!

I found the complete service manual (including wiring diagrams) for the 1990 Pathfinder and D21 pickups, and the manual for the 1994 Pathfinder/D21. Since 1992 is right in the middle of those years and probably the same generation, the wiring is probably at least mostly the same. No guarantees though. The manuals are here: www.cardiagn.com Just enter Nissan Pathfinder and scroll down to the early '90s.
 
The turn signal bulbs are a low ohm value when cold, making it difficult to troubleshoot.. Take out all of the turn signal bulbs, remove the fuse and start checking for remaining continuity with an ohm meter.
 
Replace the fuse with a wired in series 12 volt lamp or series the fuse with the same lamp. This will stop the fuse blowing and allow troubleshooting. When the lamp is brightest the path to chassis ground is most direct. Start by pulling all the lamps in the circuit, disconnecting the wiring to sockets and wiggling the cable/wire runs from the lamps back to the fuse panel. Hard to teach DC automotive troubleshooting over the internet .
 
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