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.

[LetItSnow]

On the back of the switches, the wires function as follows:

Brn & Grn/Yel - Cruise Control - Toggle
Red & Grn - Cruise Control - Indicator
Wht & Yel - Fog Lamps - Toggle
Red & Blk - Fog Lamps - Indicator
Red/Blu & White/Yel - Security Indicator
Lt Grn & Red/Blk - Security - Toggle
Orn & Blu - Whole Panel - Word Illumination

If your Fog Lamps indicator is lit, I'd assume that Wht to Yel would produce some small voltage, as the majority is consumed by the fog relay.

And hey, you're right if you said that these colors don't match those in the service manual. It wasn't my idea! These were identified from two individual sets of switches and my multitester.

[kwren]

the fog switch completes the circuit to ground for the relays for the lights. when it is depressed both wires in the ground circuit are at ground potential, consequently, no voltage would be registered.on either wire.

[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.

[LetItSnow]

Originally Posted by kwren

the fog switch completes the circuit to ground for the relays for the lights. when it is depressed both wires in the ground circuit are at ground potential, consequently, no voltage would be registered.on either wire.

Gah, negligible resistance across the switch = nearly no voltage drop, but it's there!

[ridered777]

Hmmm, so where to start...

So since I didn't know the pairing, I guess I'm going to have to go behind there and check voltages again - I measured my relative to permanent ground, there was a black ground wire back there, and I just measured absolute potential of each wire. No wonder I couldn't find any wires with power before turning the foglights on...

My foglight indicator DOES light up, thats' what baffles me as to what could be wrong with these stupid things. They went from an easy to fix to an electrical gremlin that I have neither the time nor knowledge to track down.

Thanks for the info Snow and krwen... unfortunately, I still don't know what is wrong with it and where to point the finger to in the system - I just know what ISN'T broken.

And Trevor, multimeter is the term I've been looking for . Though it would seem you mistook my statement of "When set to ammeter, it is almost no impedance, because you run the circuit "through" the instrument, that is how one measures amps." to mean that I thought there was absolutely no impedance, when I said almost. I am aware that a small amount must be produced to measure amps with - Ohms law of course. However, this amount of impedance should not affect the circuit or its operation drastically, hence the statement of "almost no".

The rest coincides with what I know, with the exception of the history lesson on previous voltmeters and "VTVM"'s .I was not aware of this, and am pleased to have acquire yet more knowledge from your seemingly limitless databases.

And as a note, my statement of "I'm just checking... if I have a voltmeters operation down wrong, then they certainly screwed up teaching me about inductors, capacitors, and transformers! " was meant to have the interpretation of that, the teachers made an error in JUDGMENT to deem myself READY to learn about aforementioned (more complex) electrical components and systems. I acquire my knowledge from a very well respected college and a more than adequate teacher- I hold no doubt the information presented was pristinely accurate.

[Hocrest]

I would find the foglight relay and check that out....

I think it's up above the pedals somewhere??? Anyone with the FSM's care to help out??

[kwren]

Originally Posted by Hocrest

I would find the foglight relay and check that out....

I think it's up above the pedals somewhere??? Anyone with the FSM's care to help out??

Pretty sure... on the side just above the carpet behind that push on panel. more information is on the way soon
Hang in there!
Keith