how do you find a short with the multimeter

Printable View

09-06-2006, 08:20 AM
SirHustlerEsq

how do you find a short with the multimeter

I should show infinit resistance when contacting each side of the fuse terminal with the probes right? Then, when I find the deadshort, and eliminate it, I should see a +-50ohm value right?

I can't seem to find my short in the "tail" circuit. I guess I will just start taking the car apart and look for a jacked up red/blk wire right?

and thanks for help.
09-06-2006, 08:44 AM
tailchaser

Quote:

Originally Posted by mr brg

I should show infinit resistance when contacting each side of the fuse terminal with the probes right? Then, when I find the deadshort, and eliminate it, I should see a +-50ohm value right?

I can't seem to find my short in the "tail" circuit. I guess I will just start taking the car apart and look for a jacked up red/blk wire right?

and thanks for help.

Try submerging your car in water and looking for the bubbles. Much faster.
09-06-2006, 08:44 AM
sammm

Check for continuity, not resistance (underwater gives faster results too).
09-06-2006, 08:47 AM
POS Racing

Quote:

Originally Posted by tailchaser

Try submerging your car in water and looking for the bubbles. Much faster.

:clap: Dang I spit coffee on my monitor and keyboard! :clap:
09-06-2006, 08:52 AM
tailchaser

also... in order to save weight... Mazda included only a VERY small amount of smoke in Miatas. If any let out because of the short, you'll need to replace that before the lights will work properly.
09-06-2006, 09:30 AM
SirHustlerEsq

Quote:

Originally Posted by sammm

Check for continuity, not resistance (underwater gives faster results too).

if I have a deadshort after the fuse box, I should be able to pull current when jumping from a power source to after the fuse box right?
09-06-2006, 09:33 AM
Dave04

Quote:

Originally Posted by mr brg

if I have a deadshort after the fuse box, I should be able to pull current when jumping from a power source to after the fuse box right?

Doing this will likely let out lots of the precious smoke that TC mentioned above...

The best way you are going to find a short in a DC system like this (especially when the common ground is the body of the vehicle) is through a visual inspection.

EDIT: on second thought... if you do what you recommend (with a big enough battery) you will quickly find the short because that's where the fire will start.
09-06-2006, 09:39 AM
SirHustlerEsq

Quote:

Originally Posted by Dave04

Doing this will likely let out lots of the precious smoke that TC mentioned above...

The best way you are going to find a short in a DC system like this (especially when the common ground is the body of the vehicle) is through a visual inspection.

EDIT: on second thought... if you do what you recommend (with a big enough battery) you will quickly find the short because that's where the fire will start.

multimeter ftw.

I guess I'll just start stripping the car since the roll bar is about to go in.
09-06-2006, 09:50 AM
POS Racing

Was it the frayed wire you found yesterday that was causing the fuse to blow??

http://forum.miata.net/vb/showthread...1&page=1&pp=25
09-06-2006, 09:50 AM
SirHustlerEsq

btw, did I mention that this totally sucks?
09-06-2006, 09:51 AM
SirHustlerEsq

Quote:

Originally Posted by POS Racing

Was it the frayed wire you found yesterday that was cousing the fuse to blow??

http://forum.miata.net/vb/showthread...1&page=1&pp=25

apparently not. I check it again today, and its still taped up. I thought that was the problem because I put another fuse it in and it worked for a day.

sorry I made a mistake. I wish I hadn't.
09-06-2006, 09:58 AM
POS Racing

Have you added anything new to the car recently??
09-06-2006, 10:05 AM
channelmaniac

Do you have an aftermarket horn?
09-06-2006, 10:24 AM
black roadster

Quote:

Originally Posted by channelmaniac

Do you have an aftermarket horn?

Yep. The horn and the tail lights share the same fuse.
09-06-2006, 10:27 AM
SirHustlerEsq

Quote:

Originally Posted by POS Racing

Have you added anything new to the car recently??

no

I have to check the horn, again...its stock btw.
09-06-2006, 10:28 AM
MadMerv

Quote:

Originally Posted by tailchaser

also... in order to save weight... Mazda included only a VERY small amount of smoke in Miatas. If any let out because of the short, you'll need to replace that before the lights will work properly.

and don't forget the mirrors!!!!!!
09-06-2006, 11:18 AM
Treibenschnell

Quote:

Originally Posted by tailchaser

Try submerging your car in water and looking for the bubbles. Much faster.

Quote:

Originally Posted by sammm

Check for continuity, not resistance (underwater gives faster results too).

Quote:

Originally Posted by POS Racing

:clap: Dang I spit coffee on my monitor and keyboard! :clap:

Same here!! :clap::clap::clap:
09-06-2006, 11:58 AM
SirHustlerEsq

just double checked...the horn does work. Atleast when I get out of work today, its like the most perfect day to have car issues. So nice outside.
09-06-2006, 01:35 PM
tailchaser

Quote:

Originally Posted by Dave04

if you do what you recommend (with a big enough battery) you will quickly find the short because that's where the fire will start.

Plus you can confirm the location by looking for bubbles after you submerse the now burning car in water... which you should have done in the first place.
09-06-2006, 01:47 PM
MadMerv

...or you could park it on I820, across from Hiley Mazda.......
09-06-2006, 02:01 PM
Treibenschnell

Quote:

Originally Posted by MadMerv

...or you could park it on I820, across from Hiley Mazda.......

::BigWhack
09-06-2006, 02:09 PM
onething

Quote:

Originally Posted by mr brg

btw, did I mention that this totally sucks?

The problem or all the help you're getting here? Please be specific . . .
09-06-2006, 02:28 PM
channelmaniac

Quote:

Originally Posted by mr brg

just double checked...the horn does work. Atleast when I get out of work today, its like the most perfect day to have car issues. So nice outside.

OK...

Horn and brake lights share the same fuse... So you have brake lights but no tail lights?

The Tail fuse powers many things in the car... It runs the front park lights, rear park lights, front & rear side marker lights, panel lights control switch (ac/heater switch lights), the ashtray light (Have you removed the console lately and pinched a wire?), the light on the radio, AND the ECU pin 1U.

A short on any of these will cause the problem.

What have you done on the car lately? Have you installed a radio? Miswiring that light wire to ground would blow the fuse when you turned on the lights. I did that once years ago on a Ford Fiesta (the 1980 model, not the newer tin can from Korea)...

Raymond
09-06-2006, 02:31 PM
POS Racing

http://forum.miata.net/vb/showthread.php?t=198601

Have you done any of the things the fine folk on Miata.net have recommended?

Tons of good information on that post!
09-06-2006, 04:56 PM
SirHustlerEsq

Quote:

Originally Posted by channelmaniac

OK...

Horn and brake lights share the same fuse... So you have brake lights but no tail lights?

The Tail fuse powers many things in the car... It runs the front park lights, rear park lights, front & rear side marker lights, panel lights control switch (ac/heater switch lights), the ashtray light (Have you removed the console lately and pinched a wire?), the light on the radio, AND the ECU pin 1U.

A short on any of these will cause the problem.

What have you done on the car lately? Have you installed a radio? Miswiring that light wire to ground would blow the fuse when you turned on the lights. I did that once years ago on a Ford Fiesta (the 1980 model, not the newer tin can from Korea)...

Raymond

I have done nothing to the car since may. I have an aftermarket radio,but the illumination wire is capped and taped, and double checked today. The interior is pretty much removed, and every inch of wire is exposed, and in good condition. I unplugged the tail lights, front lights, side lights, plate lights, and unplugged the cluster. I put the fuse in, then added each light one by one...and everything works again.

I drove it arround for a few miles and it still has not blown. I don't really know what to do next. All the wire looks clean, and everything works temporarily.

meh, this is frustrating.
09-06-2006, 05:30 PM
Treibenschnell

Ah... wiring problems... good times, good times...
09-06-2006, 05:44 PM
SirHustlerEsq

Quote:

Originally Posted by Treibenschnell

Ah... wiring problems... good times, good times...

Its funny, VW is known for hellacious electrical apocalyptic catastrophes, but strong mechanicals. I kept blowing transmissions in it but never had an electrical problem aside from sensors blowing out. Then I get the miata because I'm tired of working on the vw, and now I have electrical problems.

I guess I can just make the miata my day car, and fix the vw and drive it at night.:burnrubr:
09-06-2006, 05:58 PM
Treibenschnell

Quote:

Originally Posted by mr brg

Its funny, VW is known for hellacious electrical apocalyptic catastrophes...

Funny thing is I was talking about my Miata...

And yes, the VW has it's issues as well. :(
09-06-2006, 07:12 PM
Radio-Active

Quote:

Originally Posted by mr brg

Its funny, VW is known for hellacious electrical apocalyptic catastrophes, but strong mechanicals. I kept blowing transmissions in it but never had an electrical problem aside from sensors blowing out. Then I get the miata because I'm tired of working on the vw, and now I have electrical problems.

I guess I can just make the miata my day car, and fix the vw and drive it at night.:burnrubr:

Try FIAT X1/9

After that, all others are a walk in the park.

If it wasn't the electrical, it was the brakes.
If it wasn't the brakes, it was the fuel filter.
If it wasn't the fuel filter it was the distributor.
If it wasn't the distributor, it was the transaxle.

Man, I wished that car would have gotten stolen. :rolleyes:
Glad I don't have it anymore. I found a sucker to take it from me.::Angel::
09-06-2006, 07:48 PM
Radio-Active

Quote:

Originally Posted by mr brg

I should show infinit resistance when contacting each side of the fuse terminal with the probes right? Then, when I find the deadshort, and eliminate it, I should see a +-50ohm value right?

I can't seem to find my short in the "tail" circuit. I guess I will just start taking the car apart and look for a jacked up red/blk wire right?

and thanks for help.

Just for reference since the thread has drifted.

If anyone has a schematic diagram, it would be very helpful to find the root cause. If I recall right(and I may be way out there on this since it was over 10 years ago), when I installed my moms aftermarket radio in the 91 Miata that she had, I was blowing tail light fuses after using one of the Metra radio wiring harnesses. I came to the conclusion that the ground on the factory radio harness did not supply the necessary power needed for the accessory and main power and was able to resolve her issue.

If you had all of the tail lights out and the horn or what ever else is listed on the fuse in the manual disconnected, I would find out which side of the fuse teminals is hot and not. Then I would take the dead side terminal, after I took all of the lights out of the circuit and whatever else and touch the oher end to a good ground. If it is anything but infinite(or less that in the 10k range of resistance which can be picked up through your skin), there are either other things attached to the circuit, or there is a bare wire.