How to track a short?

[89YJBuilder]

OK I am new to vehicle electrical stuff. I have successfully wire lights and radios. I have rewired a few trailers, both with and without brakes. Ican add a brake controler. So I guess I'm not a total beginner. BUT I have a short in my rig that keeps eating Optimas. How do I start tracking this down so I can fix it. I would love to buy a new wiring harness and be done with it but I don't have that kinda money. I have a good multi meter and a few test lights. Where do I start?

[flatlander757]

Originally Posted by 89YJBuilder

OK I am new to vehicle electrical stuff. I have successfully wire lights and radios. I have rewired a few trailers, both with and without brakes. Ican add a brake controler. So I guess I'm not a total beginner. BUT I have a short in my rig that keeps eating Optimas. How do I start tracking this down so I can fix it. I would love to buy a new wiring harness and be done with it but I don't have that kinda money. I have a good multi meter and a few test lights. Where do I start?

First off: Optimas suck and that is probably the problem... see the "Optimas suck" thread

/forum/electrical-wiring/913442-batteries-optima-alternatives.html

Generally, first step is to start with a charged and known good battery... a bad one will do all kinds of goofy shit. Borrow a battery just for while you're testing this.

To check for a current drain, set your DVOM on the "amps" setting... MAKE SURE YOU HAVE THE LEADS IN THE CORRECT SPOT TO DO THIS AS WELL.... ask me how I know Make sure your dial setting is using the 15AMP fuse in the meter... NOT the pissant 5 amp fuse for measuring smaller draws. Also make sure your big fuse is GOOD... if you need to, remove it and check the fuse alone for continuity(remember leads AND dial in correct spot on meter!)... should be 0.3ohms or less.

Disconnect the negative cable of your battery.

With the leads and dial set to measure higher amperage draw(as explained above... 15A meter fuse!), put one lead on the negative cable, put one lead on the negative battery terminal. You are using the meter to bridge the battery to the cable.

DO NOT TRY TO START THE VEHICLE WHILE DOING THIS!!! It's a 15A fuse more than likely... starter will draw 200A + and kill the fuse if you're lucky, or meter if not.

Since you're talking about killing batteries... that means you do this with the KEY OFF

Give it about 3-4 minutes to stabilize and your end reading current draw should be pretty low... usually no more than 100mA. there are a million different opinions on what is "acceptable", but if you have anything running, it will show up much higher than that. I've heard everything from 20 to 100mA being acceptable myself.

It's important to wait a few minutes because whatever modules on your vehicle MAY need some time to go into "sleep" mode. I work on newer cars so this is an issue for me, I don't know what kind of turd you have pieced together Old shit shouldn't take long at all.

At that point, say you have a 2 amp draw... start removing fuses(only one at a time!) until the draw goes away... then your current drain is at least narrowed down to a circuit. From there you start testing individual components depending on what is present.

That's it in a nutshell

[89YJBuilder]

Thanks it realy helps. I think I did that kill a meter deal once as a kid playing with dads meeter that I shouldn't have been.
Well I am working on an 89 YJ with stock almost everything. Electricly two sets of lights w/ realays, a set of led tail lights, one CB, and a Via-Air, viair, oh hell how ever you spell it, on board air. Twin compresors. And the Optima.
I'll swap batteries tomarrow and start tracking this weekend. I'll leave the "new" battery disconected till I start testing.
Thanks again.

[Cooter!]

An old man trick is to do exactly what was stated above, but use a test light in series of the ground terminal, instead of an ammeter.

It won't tell you the exact amount of draw, but a test light will glow brightly at 1 amp of current.

[WildStyle]

Most manufacturers state that 0.05 amp draw is acceptable. So anything greater than that you have an issue.

[Throttleman]

Originally Posted by flatlander757

First off: Optimas suck and that is probably the problem... see the "Optimas suck" thread

http://www.pirate4x4.com/forum/showthread.php?t=913442

Generally, first step is to start with a charged and known good battery... a bad one will do all kinds of goofy shit. Borrow a battery just for while you're testing this.

To check for a current drain, set your DVOM on the "amps" setting... MAKE SURE YOU HAVE THE LEADS IN THE CORRECT SPOT TO DO THIS AS WELL.... ask me how I know Make sure your dial setting is using the 15AMP fuse in the meter... NOT the pissant 5 amp fuse for measuring smaller draws. Also make sure your big fuse is GOOD... if you need to, remove it and check the fuse alone for continuity(remember leads AND dial in correct spot on meter!)... should be 0.3ohms or less.

Disconnect the negative cable of your battery.

With the leads and dial set to measure higher amperage draw(as explained above... 15A meter fuse!), put one lead on the negative cable, put one lead on the negative battery terminal. You are using the meter to bridge the battery to the cable.

DO NOT TRY TO START THE VEHICLE WHILE DOING THIS!!! It's a 15A fuse more than likely... starter will draw 200A + and kill the fuse if you're lucky, or meter if not.

Since you're talking about killing batteries... that means you do this with the KEY OFF

Give it about 3-4 minutes to stabilize and your end reading current draw should be pretty low... usually no more than 100mA. there are a million different opinions on what is "acceptable", but if you have anything running, it will show up much higher than that. I've heard everything from 20 to 100mA being acceptable myself.

It's important to wait a few minutes because whatever modules on your vehicle MAY need some time to go into "sleep" mode. I work on newer cars so this is an issue for me, I don't know what kind of turd you have pieced together Old shit shouldn't take long at all.

At that point, say you have a 2 amp draw... start removing fuses(only one at a time!) until the draw goes away... then your current drain is at least narrowed down to a circuit. From there you start testing individual components depending on what is present.

That's it in a nutshell

He said he had a short, not a parasitic draw.

[flatlander757]

If he had a short.. he'd have a) blown fuses or b) a fire.

He has a parasitic draw. Do YOU know the difference? It is always a "short" to customers... in reality it is usually an open circuit or a parasitic draw.

[Throttleman]

Originally Posted by flatlander757

If he had a short.. he'd have a) blown fuses or b) a fire.

He has a parasitic draw. Do YOU know the difference? It is always a "short" to customers... in reality it is usually an open circuit or a parasitic draw.

OP said NOTHING about anything other than a "short" Not a word about melted wires or blown fuses. You assumed more than what he wrote. Just like I assumed the fuse had already blown and he was tracking down why the fuse blew or the wires were getting hot and smoky.

So if OP wants help using his Ohm meter to locate the SHORT he wrote about I can help, and assume you can as well.

If the OP is looking for a parasitic phantom load your post will work just fine.

Its just semantics at this point.

[flatlander757]

Originally Posted by Throttleman

OP said NOTHING about anything other than a "short" Not a word about melted wires or blown fuses. You assumed more than what he wrote. Just like I assumed the fuse had already blown and he was tracking down why the fuse blew or the wires were getting hot and smoky.

So if OP wants help using his Ohm meter to locate the SHORT he wrote about I can help, and assume you can as well.

If the OP is looking for a parasitic phantom load your post will work just fine.

Its just semantics at this point.

Err... I think I'm the only one who did use real info in his original post:

BUT I have a short in my rig that keeps eating Optimas

Shorts don't eat batteries(edit: without destroying other shit too at least). Hence my post

His symptom is eating batteries.



http://en.wikipedia.org/wiki/Short_circuit

[chimaira989]

A few extra tidbits to throw out there that I have picked up along the way..

If you have a dead short (blowing fuses), I have found it helpful to take a thermal auto resetting circuit breaker, and find a way to insert it where the fuse once resided. This allows you to work on a live circuit without melting wires and wasting a handful of fuses as you trace the circuit.

With this in place you can begin to follow the harness, unplgging each junction a step at a time until the breaker quits resetting, indicating your short has just been narrowed down to this portion of the circuit. This was helpful in finding a shorted capacitor inside the distributor on a corolla that would instantly blow both ECU fuses.

Along those same lines, if you have a draw larger than 15 amps, a DC clamp Ohm meter is extremely helpful. These used to be really expensive, and usually only found in the AC flavor, however Sears now carries one for about 60 bucks.

This can be clamped around any section of the harness and tell you exactly how many amps are flowing through the respective portion of circuit. Start pulling fuses, or disconnection electrical components till the draw drops off, as was described earlier.

Anyway, hopefully someone finds that stuff helpful. These are just some of the tecniques I have formulated working on the rolling electrical problems also known as fire trucks.

[4x4prepper]

> Where do I start?

See what wiring harness is laying on the hot exhaust or hot manifold is usually where I start. On some FWD vehicles, I head right towards the EGR. If that does not work.

If a GM then I look at the fusible links on the starter UNDER the $#%# vehicle.

If a Ford, I just feel the fusible links off the fender mounted starter relay.

The first step, looking for wires on hot stuff, solves most of the shorts and draws without even needing to pull out a DMM or test light.

Knowing the year, make, model, and motor is always nice since some vehicles have design flaws.

[rockmup]

Originally Posted by Cooter!

An old man trick is to do exactly what was stated above, but use a test light in series of the ground terminal, instead of an ammeter.

It won't tell you the exact amount of draw, but a test light will glow brightly at 1 amp of current.

The rest of this story is to start pulling fuses. When the light goes out you'll know it's in that circuit.

[89YJBuilder]

Okay thanks all you have helped me yet again. I truely appreciate it. There is "parasitic draw" not a short. One of the things that you all helped me to learn. I have 0.13 draw. So I have not gotten back to it after figuring that out. Life has gotten in the way again. Oh well it's more toy than transport. But thanks to yall I'll be able to figure it out.

[edglock21]

Subscribing

[DMG]

.13 is nothing. That would take months to kill a battery. You have a junk optima or the charging system is weak.

[R290]

Finding a short, when all else fails. I had an XJ that was blowing a fuse and I disconnected everything. Still blowing the fuse. I cut a piece of metal and stuck in the fuse slot and went looking for a fire. This is after like 3 days of messing with it. No fire, but in the rear hatch wire harness was getting warm. Turn out to be some factory grounds that are crimped together worn a hole in one of the hot wires insulation.

As for the parasitic draw, on my rig its the stuff I've added and did not tie it into Key On power. I'm doing a redo on a couple items to take care of that. Would help it I turn them off too