frame is electrically hot
Thread Starter
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Joined: Apr 2006
Posts: 75
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From: Ridge NY
frame is electrically hot
While starting to troubleshoot a number of electrical issues I discoverd my frame has 12v coming out of it!
My headlights, power windows and most dash lights, etc are working. With the negative cable disconnected, and a test light on the negative post, touching the test light to what should be a ground lights up the light. A voltmeter shows 12v. My rear compartment light recently started to stay lit with the doors closed. THis problem exists both with the key in the on position or off. Any ideas where I should look first???
thanks in advance
My headlights, power windows and most dash lights, etc are working. With the negative cable disconnected, and a test light on the negative post, touching the test light to what should be a ground lights up the light. A voltmeter shows 12v. My rear compartment light recently started to stay lit with the doors closed. THis problem exists both with the key in the on position or off. Any ideas where I should look first???
thanks in advance
Melting Slicks
Joined: Mar 2005
Posts: 2,891
Likes: 4
From: North Port Fl
Start pulling fuses one at a time and replace and then pull another to see if this fixes the problem and that could narrow it down. If it doesn't then you have a short somewhere between the battery and the fuse pannel.
Burning Brakes
Joined: Sep 2004
Posts: 1,167
Likes: 2
From: Ft.Worth Texas
Originally Posted by ljthe2nd
Start pulling fuses one at a time and replace and then pull another to see if this fixes the problem and that could narrow it down. If it doesn't then you have a short somewhere between the battery and the fuse pannel.
Le Mans Master
Joined: Nov 2003
Posts: 5,771
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From: Maryland
St. Jude Donor '05, '09, '15
Originally Posted by jfurcht
While starting to troubleshoot a number of electrical issues I discoverd my frame has 12v coming out of it!
My headlights, power windows and most dash lights, etc are working. With the negative cable disconnected, and a test light on the negative post, touching the test light to what should be a ground lights up the light. A voltmeter shows 12v. My rear compartment light recently started to stay lit with the doors closed. THis problem exists both with the key in the on position or off. Any ideas where I should look first???
thanks in advance
My headlights, power windows and most dash lights, etc are working. With the negative cable disconnected, and a test light on the negative post, touching the test light to what should be a ground lights up the light. A voltmeter shows 12v. My rear compartment light recently started to stay lit with the doors closed. THis problem exists both with the key in the on position or off. Any ideas where I should look first???
thanks in advance
Burning Brakes
Joined: Feb 2006
Posts: 1,173
Likes: 5
From: Paducah Ky
electricity will pass through the bulb that is staying lit (or anything else that has power to it continuously such as the clock), or the interior lights if you have the door open while you are doing this test. The frame would normally be 12 volt negative but with the battery cable disconnected the 12 volt passing through the path mentioned above would make the frame "hot" when measured to the neg battery post.
A better test procedure would be to get an electrical schematic for the car, identify all switches that could source power to the lamp, and disconnect them one at the time until the lamp goes out.
A better test procedure would be to get an electrical schematic for the car, identify all switches that could source power to the lamp, and disconnect them one at the time until the lamp goes out.
Melting Slicks
Joined: Mar 2005
Posts: 2,891
Likes: 4
From: North Port Fl
Originally Posted by gyopp
electricity will pass through the bulb that is staying lit (or anything else that has power to it continuously such as the clock), or the interior lights if you have the door open while you are doing this test. The frame would normally be 12 volt negative but with the battery cable disconnected the 12 volt passing through the path mentioned above would make the frame "hot" when measured to the neg battery post.
A better test procedure would be to get an electrical schematic for the car, identify all switches that could source power to the lamp, and disconnect them one at the time until the lamp goes out.
A better test procedure would be to get an electrical schematic for the car, identify all switches that could source power to the lamp, and disconnect them one at the time until the lamp goes out.
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
The frame is the returm, negative, ground path, what evever you want to call it. If you disconnect the battery negative from everything ( take the black cable off ) and things still light up you have invented something new.
If you put a test light between the negative terminal on the battery and the black cable, you are completing the circuit and if you put a meter on across the test light, positive to the black cable and negative to the negative battery cable ( with the test light still connected ) then it will look like the frame is postive, I guess, but all you are doing is measuring the voltage drop across the test light which may or may not be 12V depending on whether there is anything in series with the test light on at the same time.
If you have a light in the back that lights up with doors closed, you have a short somewhere
If you put a test light between the negative terminal on the battery and the black cable, you are completing the circuit and if you put a meter on across the test light, positive to the black cable and negative to the negative battery cable ( with the test light still connected ) then it will look like the frame is postive, I guess, but all you are doing is measuring the voltage drop across the test light which may or may not be 12V depending on whether there is anything in series with the test light on at the same time.
If you have a light in the back that lights up with doors closed, you have a short somewhere
Last edited by MotorHead; Jun 17, 2006 at 11:52 PM.
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Burning Brakes
Joined: Feb 2006
Posts: 1,173
Likes: 5
From: Paducah Ky
Originally Posted by ljthe2nd
I don't know what you are trying to say here, there is no such thing as 12v negative, in DC the frame is alway grounded with the negative wire from the battery attached. If you disconnect the ground wire from the battery to the frame, it is nothing just a conductor, but if you connect a 12 v source to the frame with no ground you will still have no current flow, no voltage
this lamp is grounded to the frame. When he removed the negative battery cable from the battery the lamp went out because there was not a complete electrical path the 12 volt positive will now pass through the unlit bulb to what was the negative side or in this case, the frame. If you now measure from the frame to the battery negative post you will read 12 volts. By the way, it takes both a positive and a negative to make DC voltage. The DC negative side is commonly referred to as ground but if you look at the battery it is clearly marked "negative".
Melting Slicks
Joined: Mar 2005
Posts: 2,891
Likes: 4
From: North Port Fl
Originally Posted by gyopp
He said that his rear compartment lamp is staying on.
this lamp is grounded to the frame. When he removed the negative battery cable from the battery the lamp went out because there was not a complete electrical path the 12 volt positive will now pass through the unlit bulb to what was the negative side or in this case, the frame. If you now measure from the frame to the battery negative post you will read 12 volts. By the way, it takes both a positive and a negative to make DC voltage. The DC negative side is commonly referred to as ground but if you look at the battery it is clearly marked "negative".
this lamp is grounded to the frame. When he removed the negative battery cable from the battery the lamp went out because there was not a complete electrical path the 12 volt positive will now pass through the unlit bulb to what was the negative side or in this case, the frame. If you now measure from the frame to the battery negative post you will read 12 volts. By the way, it takes both a positive and a negative to make DC voltage. The DC negative side is commonly referred to as ground but if you look at the battery it is clearly marked "negative".
Melting Slicks
Joined: Mar 2005
Posts: 2,891
Likes: 4
From: North Port Fl
And I agree with everyone that is saying he is completing the circuit with his test light giving him the false impression that he has 12 volts running through his frame, so if he hooks up his test light or meter to the frame and negative battery terminal and pulls one fuse, and replaces it and then pulls the next fuse and does this he will most likely find out what circuit he needs to look at to find the short.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Originally Posted by jfurcht
While starting to troubleshoot a number of electrical issues I discoverd my frame has 12v coming out of it!
My headlights, power windows and most dash lights, etc are working. With the negative cable disconnected, and a test light on the negative post, touching the test light to what should be a ground lights up the light. A voltmeter shows 12v. My rear compartment light recently started to stay lit with the doors closed. THis problem exists both with the key in the on position or off. Any ideas where I should look first???
thanks in advance
My headlights, power windows and most dash lights, etc are working. With the negative cable disconnected, and a test light on the negative post, touching the test light to what should be a ground lights up the light. A voltmeter shows 12v. My rear compartment light recently started to stay lit with the doors closed. THis problem exists both with the key in the on position or off. Any ideas where I should look first???
thanks in advance
Last edited by ...Roger...; Jun 18, 2006 at 12:57 AM.
Instructor
Joined: Nov 2004
Posts: 162
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Originally Posted by ljthe2nd
I didn't understand you, that's exactly what I was saying there is no such thing as 12v negative in DC there is positive and negative or ground, the positive can be what ever voltage the supply is but there is no such thing as negative voltage in a simple DC circuit.
Melting Slicks
Joined: Mar 2005
Posts: 2,891
Likes: 4
From: North Port Fl
Originally Posted by rick1500
Do you mean in car-land or in any DC circuit? It's been a few years, but I can remember solving many electrical engineering homework problems where the answer involved a negative voltage in a DC circuit. Voltage measurements are relative, so they can technically be negative depending on how you choose to measure them (my DC voltmeter has a minus sign for that reason).
Instructor
Joined: Nov 2004
Posts: 162
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Originally Posted by ljthe2nd
We are talking about this guys car, and you guys want to get off the subject, if you don't have something constructive to add, don't reply, this is one of the rules of this forum
jfurcht, if you remove the rear compartment light's bulb and hook up your test light the same way, do you still get the test light lighting up? If not, then you've localized the problem to the rear compartment light's circuit and you should go with gyopp's advice: look at a schematic and remove any suspect switches or other potential shorts in the rear compartment light's circuit. I'd do that simple test before pulling fuses out at random.
Good luck! I rebuilt a Triumph years ago...at least you're not dealing with Lucas electronics!
Thread Starter
Advanced
Joined: Apr 2006
Posts: 75
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From: Ridge NY
thanks for the replies so far.
To answer some questions, the car is a 76, ther is no interior light delay.
The light was working fine, on and off with the doors, then one day it just stayed on. While troubleshooting that problem is when I noticed the frame was hot. I will be working on the problem during the next few evenings during the week and I will try some of the groups suggestions and report back.
thanks again for the help
To answer some questions, the car is a 76, ther is no interior light delay.
The light was working fine, on and off with the doors, then one day it just stayed on. While troubleshooting that problem is when I noticed the frame was hot. I will be working on the problem during the next few evenings during the week and I will try some of the groups suggestions and report back.
thanks again for the help
Burning Brakes
Joined: Jul 2001
Posts: 853
Likes: 0
From: Foxfield, Co
Originally Posted by jfurcht
thanks for the replies so far.
To answer some questions, the car is a 76, ther is no interior light delay.
The light was working fine, on and off with the doors, then one day it just stayed on. While troubleshooting that problem is when I noticed the frame was hot. I will be working on the problem during the next few evenings during the week and I will try some of the groups suggestions and report back.
thanks again for the help
To answer some questions, the car is a 76, ther is no interior light delay.
The light was working fine, on and off with the doors, then one day it just stayed on. While troubleshooting that problem is when I noticed the frame was hot. I will be working on the problem during the next few evenings during the week and I will try some of the groups suggestions and report back.
thanks again for the help
Greg.