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  #1  
Old 04-14-2013, 03:36 PM
Littleman456 Littleman456 is offline
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Default Tracing down a short. Any tips?

In all fairness I probably shouldn't of expected a $350 truck to run in the rain, but anyway: went to start the truck today in the rain (was running and driving just fine yesterday) and it only turned over a handful of times before the battery died. Odd seeing as its a new battery. Went to jump start it and noticed a loose serpentine belt! Must not have been charging, easy fix. Tighten it up, and when I hooked up that jumper cables sparks everywhere. Alright, disconnect all the cables, dry off all the contacts and try it again in a different order, sparks everywhere. Long story short using a multimeter on continuity setting I get near perfect continuity between my battery positive and negative. Great. Followed the positive up around the radiator to a plug on top of the driver's front fender and unplugged it. No more continuity between battery posts. Dang, that woulda been easy. Next I checked two black 16ga fusible links one on an orange and one on a white wire. Both have continuity to ground. Anyone have any suggestions on where I should look? Is there a common weak spot in the early ranger's wiring I should check? Any help is much appreciated. Truck is an 84 standard cab that cam with a 2.0 and now has what is thought to be an 80 engine out of?. Lots of extra sensors and vacuum lines (coming from box on passenger fender). Anywhere I should specifically check? No fuses are blown so I can't imagine it's in the wipers/lighting/heating system anywhere. Thanks.
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  #2  
Old 04-14-2013, 11:27 PM
Hot Rod Roy Hot Rod Roy is offline
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Default Re: Tracing down a short. Any tips?

When you said "using a multimeter on continuity setting I get near perfect continuity between my battery positive and negative" I about dirtied my pants! If you did what you said, you would have seen plenty of sparks and smoke!! How can I trust that you know what you're doing with a comment like that?? Good luck to you!!!


Last edited by Hot Rod Roy; 04-14-2013 at 11:30 PM.
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  #3  
Old 04-14-2013, 11:34 PM
AmericanPride! AmericanPride! is offline
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Default Re: Re: Tracing down a short. Any tips?

Quote:
Originally Posted by Hot Rod Roy View Post
When you said "using a multimeter on continuity setting I get near perfect continuity between my battery positive and negative" I about dirtied my pants! If you did what you said, you would have seen plenty of sparks and smoke!!
Uhh...no you wouldn't. I don't even know how many times my leads have been on the +&- before.

I wouldn't have hooked my $500 worth of meter & leads if that would happen. Maybe with the $5 harbor freight one you use? Don't know
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  #4  
Old 04-14-2013, 11:39 PM
Hot Rod Roy Hot Rod Roy is offline
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Default Re: Tracing down a short. Any tips?

"on continuity setting"??? That's checking ohms, not volts.
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  #5  
Old 04-14-2013, 11:47 PM
AmericanPride! AmericanPride! is offline
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Default Re: Re: Tracing down a short. Any tips?

Quote:
Originally Posted by Hot Rod Roy View Post
"on continuity setting"??? That's checking ohms, not volts.
No...that setting is for continuity. If a circuit has continuity it means they're touching. Like testing a fuse. Good fuse has continuity... blown doesn't

Impedance is for OHMs
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  #6  
Old 04-14-2013, 11:56 PM
AmericanPride! AmericanPride! is offline
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Default Re: Tracing down a short. Any tips?

Impedance/ Ohms is just below the range and continuity is right of it

OP...that's a pretty old truck with apparently non stock this and that. I would start with a repair manual for stock. They have a ton of trouble shooting, plus you can possibly figure out what has been changed.

Good investment for $25
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  #7  
Old 04-15-2013, 04:03 AM
Littleman456 Littleman456 is offline
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No smoke/spark can from the multimeter, just from the jumpers, lots of spark/smoke came from those. I have a repair manual and it seems the wiring harness is about the same. The battery was putting out less than half a volt so I disconnected the battery and checked continuity from there. In hindsight I should've said that I checked the terminals. I do only have a $25 multi-meter because I was afraid I'd fry a nice one. I'm pretty good with electrical schematics, I'm just used to fluid power ones and the ones out of the manual are a bit different. Does anyone know where the first two fusible links are coming off the positive wire? Ones 14ga and ones 16. I figure the short has to be before those otherwise they would've blown, right?

P.S. I hate these rubber molded fusible links!
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  #8  
Old 04-16-2013, 12:09 PM
Littleman456 Littleman456 is offline
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Here's where I'm at.

No key
-no dome light fuse
-headlights turned off
-infinite ohms

No key
-door closed
-headlights off
~5ohms

No key
-door open
-headlights off
~1.4ohms

No key
-door open
-no dome light bulb
-Headlights off
~5ohms

Key turned to any position
~14 ohms

Key turned to any position
-headlights on
~.8 ohms

Any input would be greatly appreciated. I'm not exactly sure what's activated when the key is turned to accessory, I'd imagine just the radio and some light (when the door is open) right? Maybe it has something to do with the radio.

No change when the radio fuse is pulled.
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1985 4.6L Roadster
Bought not built. (not yet at least)

Fueled by two stroke, dr.pepper, and Hank Williams.
You can fix anything with a welder and an angle grinder

Last edited by Littleman456; 04-16-2013 at 12:14 PM.
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  #9  
Old 04-16-2013, 07:26 PM
mecman99 mecman99 is offline
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Default Re: Tracing down a short. Any tips?

Quote:
Originally Posted by AmericanPride! View Post
No...that setting is for continuity. If a circuit has continuity it means they're touching. Like testing a fuse. Good fuse has continuity... blown doesn't

Impedance is for OHMs
what does this mean.. whats touching .. electrons.. and what does Impedance is for OHMs mean?
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  #10  
Old 04-16-2013, 07:38 PM
Littleman456 Littleman456 is offline
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Ohms is resistance.


After pulling the dash, headlight switch, fuse panel, and random parts of the wiring harness apart several times I just got pissed and threw the battery back in. It runs! Not sure what the problem was but it's not charging at the moment so I'm gonna get the alternator tested tomorrow. Luckily I have a boat battery I can bring with me for the day to get to and from school. Thanks for the help!
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1985 4.6L Roadster
Bought not built. (not yet at least)

Fueled by two stroke, dr.pepper, and Hank Williams.
You can fix anything with a welder and an angle grinder
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  #11  
Old 04-16-2013, 07:43 PM
Little Blue Little Blue is offline
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Default Tracing down a short. Any tips?

Check your grounds. That's the single most common electrical issue in cars.
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  #12  
Old 04-17-2013, 06:38 PM
sheltonfilms sheltonfilms is offline
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Default Re: Tracing down a short. Any tips?

Quote:
Originally Posted by mecman99 View Post
what does this mean.. whats touching .. electrons.. and what does Impedance is for OHMs mean?
Continuity means that the two points being measures have the same voltage potential and also there is almost no resistance (because it is next to impossible to achieve zero resistance in a wire) between the two points. This can also be called a node.

Ohms is a measure of resistance, which is the opposition to the flow of current.

Look at the Ohms law:

V=RI
where voltage=resistance*current

Since this is an automotive DC system V is almost always 12V (except for voltage supplied to sensors which is 5 V).

The higher the resistance the less current and vise versa.

Now Impedance is a measure of resistance mostly used in AC circuits. It has a magnitude and phase angle. In DC circuits the angle is always 0 degrees so you only see magnitudes.

Because of the nature of coils (inductors) and capacitors, these elements have impedance.

When the elements have only DC current applied the capacitor acts as an open circuit and the inductor acts like a short circuit.

Thats just a bunch of information thrown out there. I could write about 20 pages worth covering more details that would confuse the hell out of you, but I hope that somewhat helps.
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  #13  
Old 04-19-2013, 11:23 PM
Hot Rod Roy Hot Rod Roy is offline
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Default Re: Tracing down a short. Any tips?

And that's exactly how Littleman got his truck running again! Good job Littleman!

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  #14  
Old 04-19-2013, 11:37 PM
96_4x4_XLT 96_4x4_XLT is offline
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Pro tip #32: don't suck
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