Yay for electrical problems!

[ridered777]

Question for the electrically inclined on the board....

I had a blown fog light, so I replaced them. Just before replacing them, I pulled the switch panel that has the fog-light switch among other things... This was in late fall. I wanted to see if I could get at the bulbs in there, the little green ones, you know.

Well anyway, since doing those aforementioned things, my fog-lights don't want to work. Pulled the new bulbs to check the filament, and they look fine. Threw a voltmeter on it, and I got .2v... I'm not sure what the reading is supposed to be, but I expected to find 0v, and it would mean a wire is loose or shorting. What could be causing it to read only .2v?? Any ideas on fixing it?

Its not pertinent... it's just bugging me, and when I have a warm day I want to go out and tinker with it. I was hoping someone might have experiance a similar problem...?

[TomsSVX]

check the switch to make sure it is completing the circuit first. Then follow the wiring from the switch to the relay, then to the lights to find out where it is fouling the connection

Tom

[Trevor]

Originally Posted by ridered777

Question for the electrically inclined on the board....

I had a blown fog light, so I replaced them. Just before replacing them, I pulled the switch panel that has the fog-light switch among other things... This was in late fall. I wanted to see if I could get at the bulbs in there, the little green ones, you know.

Well anyway, since doing those aforementioned things, my fog-lights don't want to work. Pulled the new bulbs to check the filament, and they look fine. Threw a voltmeter on it, and I got .2v... I'm not sure what the reading is supposed to be, but I expected to find 0v, and it would mean a wire is loose or shorting. What could be causing it to read only .2v?? Any ideas on fixing it?

Its not pertinent... it's just bugging me, and when I have a warm day I want to go out and tinker with it. I was hoping someone might have experiance a similar problem...?

An exact comment requires advice as to where you "threw" the voltmeter and the type of meter.

It would a appear that you are using a high impedance digital instrument which will give a reading as if volts are present, due to inductance or very slight leakage. In which case take the reading as indicating no voltage on a practical basis.

"Among other things", it surely obvious that you have upset something.

[ridered777]

Originally Posted by Trevor

An exact comment requires advice as to where you "threw" the voltmeter and the type of meter.

It would a appear that you are using a high impedance digital instrument which will give a reading as if volts are present, due to inductance or very slight leakage. In which case take the reading as indicating no voltage on a practical basis.

"Among other things", it surely obvious that you have upset something.

Hmm. Well I inserted the (+) lead to where I disconnected the H3 bulb (positive lead from car to fog-light). I couldn't get a good negative in the socket, so I grounded it on the negative terminal of the battery.

As far as the type, its an older radioshack voltmeter/ammeter/impedance measurement device.

I can understand negligible interference from the device if I was picking up something minute in the circuit - less than 1/10th of a volt say. But given the accuracy of the device in the past, I don't think it is the device - perhaps there is a partial short somewhere?

It is obvious I've upset something. I'm hoping I go behind the dash and find that I snapped a wire off on said switch, and its as easy as some splicing, soldering, and wrapping. I am fairly decent at electronics and wiring - it's the diagnosis that scares me if there isn't an obvious problem.

But alas, I need to leave for class.

[kwren]

maybe one of the little wires broke off at the switch. Happened to me and my fog lites wouldn't work till I soldered the little wire back on
Just a thought
Keith

[Trevor]

[QUOTE=ridered777;521401
As far as the type, its an older radioshack voltmeter/ammeter/impedance measurement device.

I can understand negligible interference from the device if I was picking up something minute in the circuit - less than 1/10th of a volt say. But given the accuracy of the device in the past, I don't think it is the device - perhaps there is a partial short somewhere?

[/QUOTE]

I was not suggesting that there is anything wrong with your meter, but rather that you could be using a one with a high input impedance and therefore of high sensitivity, typical of a digital multi meter. If you are using a low impedance analogue instrument, this could be indicating an existing series resistance but not a short circuit to ground.

You have now proven that there is no voltage at the lamp, so that as Keith has pointed out the switch or wiring must be faulty. Check for volts at the input and output of the switch.

[ridered777]

OK guys, I'll give that a shot, thanks.

On a separate note, Trevor, I thought, or I was taught at least, that any voltmeter is high impedance only in a series circuit. When set to ammeter, it is almost no impedance, because you run the circuit "through" the instrument, that is how one measures amps.

When set to measure resistance, it is not important, because you dont measure resistance with current applied to the circuit.

Is this correct? I'm just checking... if I have a voltmeters operation down wrong, then they certainly screwed up teaching me about inductors, capacitors, and transformers!

[ridered777]

Alright. Now I'm getting p-eed off.

The car and I are officially fighting, for the record. I have some time before work, so I went out to take a peek, since its the warmest day we'll have for a month I bet (40*F, whoa!), and found absolutely nothing. Everything is wired tightly. I started it up, and took readings, and, when the foglight switch and headlights are on, just about ever wire is "hot". (Which I suppose is good, because it means my switchbox isn't broken).

I took several pictures of the wires back there - anyone know which one supplies the power to the foglights? My money is on the red one directly behind the foglight switch, putting out 6.5v, just a guess though.

So now I need to go hunting deeper I suppose? The only thing that surprised me is a yellow wire behind the fog light switch was NOT hot when the foglight switch was depressed - and usually yellow is used for "accessory", or it means its the output when the switch is closed, creating a circuit.

If anyone can shed some light on to what each wire corresponds to, it would be greatly appreciated. Hmm, I wish there was a way to put the picture in the thread, so people don't have to manually open it.

Pictures are blurry, but in the first one, you can really see the red and yellow wires which I am talking about. They're just about in the center of the switchbox.

[Trevor]

Originally Posted by ridered777

OK guys, I'll give that a shot, thanks.

On a separate note, Trevor, I thought, or I was taught at least, that any voltmeter is high impedance only in a series circuit. When set to ammeter, it is almost no impedance, because you run the circuit "through" the instrument, that is how one measures amps.

When set to measure resistance, it is not important, because you dont measure resistance with current applied to the circuit.

Is this correct? I'm just checking... if I have a voltmeters operation down wrong, then they certainly screwed up teaching me about inductors, capacitors, and transformers!

Craig,

I can only assume that when you where taught you did not correctly assimilate the information provided.

A voltmeter is a voltmeter and a multi meter is I gather that to which you are referring. When set to a range to measure amps, a multi meter is in fact an ammeter and as such measures voltage developed across a shunt resistance, imposed in series with the circuit under test.

You say "When set to ammeter, it is almost no impedance, because you run the circuit "through" the instrument, that is how one measures amps." This is incorrect. When set in an amps range. a low resistance shunt is connected cross the input through which the test current passes. In fact in this mode the instrument exhibits a very low impedance/resistance. If the impedance/resistance was high this would be in series with the circuit under test, resulting in an error in the reading. What is more the instrument would be called upon to dissipate power. Refer Mr, Ohms for a definitive opinion.

Crude analogue automotive ammeters are in a different ball park and exhibit the specially low resistance of an associated internal element, which directly operates a moving iron pointer arrangement.

You say “any voltmeter is high impedance only in a series circuit.” The method of connecting a voltmeter in no way affects the integral construction or internal resistance of a given instrument. The internal resistance of voltmeters in general is dependant on the method of construction and principle of operation, there being many different types.

Analogue instruments as such, normally require that a pointer must be driven from the measured supply. This requires power to be taken from the supply under test and this can result in an incorrect reading when the test circuit is limited in respect of available current. The higher the impedance of the instrument and sensitivity of the movement, the less resistance applied across the circuit under test and the greater the inherent accuracy.

In the past vacuum tube voltmeters (VTVM) were used as high impedance instruments in order to overcome this problem. Currently solid state technology has provided a means of simple amplification and a digital readout, all operated/suppled from an inbuilt dry battery. As a general rule these instruments have a characteristic of very high impedance.

It is likely that it has been your learning and interpretation which is at fault rather than the teaching. If not, pass on this advice from one whose Company produced electrical measuring devices of all types.

[kwren]

Originally Posted by ridered777

Question for the electrically inclined on the board....

I had a blown fog light, so I replaced them. Just before replacing them, I pulled the switch panel that has the fog-light switch among other things... This was in late fall. I wanted to see if I could get at the bulbs in there, the little green ones, you know.

Well anyway, since doing those aforementioned things, my fog-lights don't want to work. Pulled the new bulbs to check the filament, and they look fine. Threw a voltmeter on it, and I got .2v... I'm not sure what the reading is supposed to be, but I expected to find 0v, and it would mean a wire is loose or shorting. What could be causing it to read only .2v?? Any ideas on fixing it?

Its not pertinent... it's just bugging me, and when I have a warm day I want to go out and tinker with it. I was hoping someone might have experience a similar problem...?

If you check the fog lights for voltage from the connectors on the filaments to ground and do not get 12 volts with your fog light switch on the dash off, you probably have a blown fuse.
reason.......... there is always a 12 volt supply to the fog lights, even with the ignition switch off.
Don't give up on this thing!!
Keith

[ridered777]

Originally Posted by kwren

If you check the fog lights for voltage from the connectors on the filaments to ground and do not get 12 volts with your fog light switch on the dash off, you probably have a blown fuse.
reason.......... there is always a 12 volt supply to the fog lights, even with the ignition switch off.
Don't give up on this thing!!
Keith

Keith, I will check the fuses, that I know I can do.

Trevor, I states in my original post that it "is just bugging me, so I thought I would weight some ideas". I made no false statments about spending countless hours hunting down this electrical bug - they're just foglights for crying out loud. I really wanted to fix them, because I want to swap them over to HID's to match the low-beams. I will quote my original post "Its not pertinent... it's just bugging me, and when I have a warm day I want to go out and tinker with it. I was hoping someone might have experiance a similar problem...?".

You have yourself commented several times in this thread on my general incompetence regarding electrical components and terminology. I never claimed any expertise in this field - if I felt I was an expert, I would not have asked anyone else's help!

I'm sorry if I make people feel cast-aside with my decision, but I already know that this electrical system is way over my head - I like working on the old 60's cars, before even EFI, I can do that kind of electronics. Looking at the wiring diagram for this car makes my head spin, I have but one year of Electrical Engineering at the college level, under my belt.

I will check the fuses tomorrow when I have sunlight, thanks for the tip. Unfortunately, I think the problem might be deeper - If I had a blown fuse, wouldn't the "indicator" light not light up on the switch? It is certainly worth a shot. I will also keep my eyes out for things that could be ary with the system. But if it is this in-depth, I am not ripping apart the interior of my only car to track down an issue with the foglights - perhaps when I do the 5spd swap in the summer.

[kwren]

Originally Posted by ridered777

Keith, I will check the fuses, that I know I can do.

I will check the fuses tomorrow when I have sunlight, thanks for the tip. Unfortunately, I think the problem might be deeper - If I had a blown fuse, wouldn't the "indicator" light not light up on the switch? It is certainly worth a shot. I will also keep my eyes out for things that could be ary with the system. But if it is this in-depth, I am not ripping apart the interior of my only car to track down an issue with the foglights - perhaps when I do the 5spd swap in the summer.

Of course, naturally, on our SVX's the "indicator" light actually uses a different power supply. It really does. no kidding.
Seriously Craig, getting your fog lights to work is not going to be a major thing.
Lets use a little logic here and get you going! I find that almost without exception that when we tackle a little job, complete it and something doesn't work that was working before we started, we are probably the reason.
Looking at your original post, you wanted to replace the bulbs for the fog lites because only one didn't work, right?
You did that and took a look at the switch in the dash as well. All back together, and not even one fog light works.

Lets consider the possibilities. Since there is 12 volts to the fog lights even without the ignition switch on, any of us could unknowingly touch something
that could blow a fuse while in the process of replacing the bulbs.
Checking for 12 volts at the fog lights will take care of that condition, either by finding that a fuse is blown, or that we are going to the next step.

I assume, and rightly so, that you replaced the lamps properly and pushed the quick disconnects together when finished replacing the bulbs.

while taking the fog light switch out on the dash, because of the brittle little wires on the switch, it would be easy to end up with one broken off of the switch.
I mentioned to you earlier, that did happen to me when I took out my switch.

For the next step, I would disconect the negative battery cable-before starting.

I recommend taking a careful look at the switch and close attention to the yellow and white wires in the center of the switch. They are the only ones we are concerned with at this time. Just making sure they are both still intact.
These are easy things to do and if a wire is not intact, it will have to be carefully soldered back.

I really believe that carefully following these suggestions will bring you another success story to put in your diary!

Hope this helps,
Keith