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Discussion Starter · #1 ·
Hello,

I am gonna ask the unasked stupid question, and I feel pretty damned stupid asking it...

Several times while trying to track down a wire or circuit, I find myself saying quite out loud, "What the f...?"

I often find both leads of a switch or component BOTH leading to ground, or to hot. This has been happening to energized and non-energized circuits.

How in the hell can I check for shorts or trace circuits?

Thanx
 

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most of time (but not all the time) when doing "in circuit" testing, either one or both (or all) ends must be disconnected to get a valid reading on the item being checked...

Les
 

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It's either a gift or a curse to understand electrical circuits, depending on which side of it you're on. The basic thing to understand is electricity is like plumbing, what goes in has to come out somewhere. Les is right, sometimes you have to isolate the circuit to test it.
 

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You may not understand this but most electrical circuits are looking for ground.

When the positive shows a reading to ground, chances are, that part of the circuit is working. Think of it like a household table lamp. If you have a light bulb in the socket and you do a resistance check on both prongs that plug into the wall, you have just verified the wiring is good on your lamp. Same thing with your bike. Your circuit might have gone through some light bulbs or something.
 

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Digital multimeters are renowned for giving "phantom" readings because they load the circuit under test so lightly. Filament light globes and some ignition coils are a particular problem because they look like short circuits to a digital meter. In fact the continuity test function of many meters (with the beep) can make just about any automotive circuit appear as a short to the novice. You need to isolate the circuit under test to get reliable readings. Failing that, an old fashioned test light can help, as it loads the circuit and provides, for the most part, an unambiguous indication of whether your circuit is hot, ground or somewhere in between.
 

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Discussion Starter · #7 ·
True ... I have a *VERY* basic understanding of electricity - DC moreso than AC maybe.

Regardless, I should be able to see which side of a single filiment bulb socket goes to ground, or how much DC voltage it is getting. This happens on both bikes.

When I put a multimeter to a simple circuit, I cannot easily determine ground via continuity. Usually, I get continuity to ground on both sides, which would normally indicate a short. Yet, the circuit functions perfectly. This is with every simple circuit I have tested so far.

And when testing DCV, the meter fluctuates wildly, as if I were testing an AC circuit in DC mode.

I tried different multimeters with the same results. I cannot possibly isolate circuits- especially if I am checking live voltage or simply trying to determine which wire is ground.

What is making the circuits act like that?

Anybody?

PS- I have never seen this in automotive circuits before- admittedly it has been maybe 20 years ago. Could it be the on board computers, etc?
 

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...How in the hell can I check for shorts or trace circuits?...
I do 99.9% of my circuit debugging using both the following:
1) Self-powered test light
2) Non-powered test light
 

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Discussion Starter · #9 ·
I have an old 12VDC test light around here somewhere... I will have to try to find it.

But, that will only show a live circuit, not the voltage amount, nor tell me which is ground.

If I rig up a simple continuity tester, you think that might work?

And yet, how do I test the voltage amount? Admittedly all my meters are digital. Should I get an analog meter?

Thanx!
 

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And when testing DCV, the meter fluctuates wildly, as if I were testing an AC circuit in DC mode.

I tried different multimeters with the same results. I cannot possibly isolate circuits- especially if I am checking live voltage or simply trying to determine which wire is ground.

What is making the circuits act like that?

Anybody?

PS- I have never seen this in automotive circuits before- admittedly it has been maybe 20 years ago. Could it be the on board computers, etc?
Is that on a brake light with a wig-wag modulator?
 

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Discussion Starter · #11 ·
Multiple different circuits, on two different bikes.
 

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... 12VDC test light... will only show a live circuit, not... tell me which is ground...If I rig up a simple continuity tester, you think that might work?..
> Hook your (non-powered) 12V test light to positive on battery, then probe around anywhere to find ground.
> Or disconnect both battery terminals; connect a self powered test light to negative battery lead wire, then probe around anywhere to find ground on a non-live circuit.

...how do I test the voltage amount? Admittedly all my meters are digital. Should I get an analog meter?...
> Connect meter leads to battery terminals... if you get 12V there, then there's typically not much need to check voltage anywhere else, just continuity.
 
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