test light

built

Dragway Regular
Apr 15, 2005
979
0
0
ohio
I keep blowing fuse's, A guy told me to test with a pen light tester by putting on end on each clip where the fuse would go and if it lights up there is a short somewhere.

Is this correct ? it seems like curent should go through to the other side , thats what a fuse does right? it blows when the current gets too high or too high of amps for the fuse rating right?
 

chevycopcar

Pro Stocker
Jul 19, 2004
1,494
0
0
S. Holland, IL
Just because it lights doesn't necessarily mean it's shorted, it just means that there's a current draw on that circuit. You would be completing the circuit with the light.
 

built

Dragway Regular
Thread starter
Apr 15, 2005
979
0
0
ohio
So say i have the door open and the dome light is on, if i take out the fuse for the dome light and put a test light across the two connections where the fuse was , should the light come on ? so if i take the dome bulb out the test light should go out too if everything is good?

To use the test light i don't put one end to ground and one end to a wire or clip right ? But to both ends of where the fuse would be correct?
 

chevycopcar

Pro Stocker
Jul 19, 2004
1,494
0
0
S. Holland, IL
built said:
So say i have the door open and the dome light is on, if i take out the fuse for the dome light and put a test light across the two connections where the fuse was , should the light come on ? so if i take the dome bulb out the test light should go out too if everything is good?

To use the test light i don't put one end to ground and one end to a wire or clip right ? But to both ends of where the fuse would be correct?

That is correct. You'll probably need a test pin or something for the gator clip end of the light, though.
 

built

Dragway Regular
Thread starter
Apr 15, 2005
979
0
0
ohio
Hmm

Can you explain to me why you put the test light ends to both sides of the fuse clips and how that tells you of a short circuit?

thanks.
 

LS6 Tommy

MalibuRacing Junkie
May 15, 2004
15,847
1
38
North Jersey
Re: Hmm

built said:
Can you explain to me why you put the test light ends to both sides of the fuse clips and how that tells you of a short circuit?

thanks.

In your example of the dome light, the 12 VDC + comes from the battery to the fuse block, through the fuse, then the bulb in the dome, to the door switch to ground. When you replace the fuse with the test light, one lead is to 12 VDC + and the other to ground. If the swtich is open, you have no circuit and the test light is not lit. If there's a short to ground, you complete the circuit and the test light lis lit.

The dome light is not a good example because the door switch is last in the circuit before the ground.

If the door is closed, the bulb is not in the dome light and the test light is is not lit, it should not light if you open the door. If it does, there's a short across the dome light itself to the switch. If the test light is lit with the door open or closed, the dome light feed is shorted to ground.

If the ignition is off, and the circuit you're testing is "hot" at all times, the switch to that accessory is "off" and the test light is lit, that tells you is that there is a short to ground between the test light and the switch in that circuit. If the switch for that circuit is "off" & you blow the fuse when you turn it "on", you have to disconnect the battery and start checking for shorts in the rest of the circuit with a continuity meter. If the circuit is "hot with ignition on", the switch for the accessory is "off" and the test light is lit, there could be shorts anywhere between the fuse block, the steering column on to the accessory's switch.

I know that's a lot to swallow. Electrical troubleshooting's a lot easier to do than to explain.

Tommy
 

built

Dragway Regular
Thread starter
Apr 15, 2005
979
0
0
ohio
Thanks Tommy, I appreciate your help alot.
I kept blowing fuses and my radio wouldn't work.
So I used a test light to avoid blowing more fuses to find the problem.
The circuit turned out to have the radio/dome/license plate light together.
I wasn't sure if i could find the problem this way or not and i wasn't sure i was connecting it right.
I put both test light leads to the ends of the fuse connectors one on each side. correct ?

I replaced the dome light bulb and the license plate bulb and it stopped blowing fues's and everything works good now.
But i am confused about how i should have tested the problem and if i did it right at all.
I took out the dome bulb because i figured with the door open it would light up the tester and i was thinking it was a loose wire behind the radio.
I hope you understand what i'm saying,lol.
 

355_79bu

Dragway Regular
Dec 13, 2005
1,240
0
0
Cotter, AR
Re: Hmm

LS6 Tommy said:
built said:
Can you explain to me why you put the test light ends to both sides of the fuse clips and how that tells you of a short circuit?

thanks.

In your example of the dome light, the 12 VDC + comes from the battery to the fuse block, through the fuse, then the bulb in the dome, to the door switch to ground. When you replace the fuse with the test light, one lead is to 12 VDC + and the other to ground. If the swtich is open, you have no circuit and the test light is not lit. If there's a short to ground, you complete the circuit and the test light lis lit.

The dome light is not a good example because the door switch is last in the circuit before the ground.

If the door is closed, the bulb is not in the dome light and the test light is is not lit, it should not light if you open the door. If it does, there's a short across the dome light itself to the switch. If the test light is lit with the door open or closed, the dome light feed is shorted to ground.

If the ignition is off, and the circuit you're testing is "hot" at all times, the switch to that accessory is "off" and the test light is lit, that tells you is that there is a short to ground between the test light and the switch in that circuit. If the switch for that circuit is "off" & you blow the fuse when you turn it "on", you have to disconnect the battery and start checking for shorts in the rest of the circuit with a continuity meter. If the circuit is "hot with ignition on", the switch for the accessory is "off" and the test light is lit, there could be shorts anywhere between the fuse block, the steering column on to the accessory's switch.

I know that's a lot to swallow. Electrical troubleshooting's a lot easier to do than to explain.

Tommy

:shock: confused_swirl.gif I would have had everyone screwed up if I'd tried explaining that. :lol:
 

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