Understanding electrical wiring....

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gregnash

gregnash

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I consider myself a fairly intelligent person (need to be somewhat intelligent to gain an MBA, but then again I work for the state government so that could be an oxy-moron!!) but electrical is something that has always stumped me.

I just recently picked up a multimeter to help diagnose why my back defogger isnt working at all but really am lost as to how to "properly" use it and diagnose my issue.

In the future I plan to add things like: OBA, SLCFJ62 Ultimate panel, extra lights, extra internal plugs for USB charging, possibly a small HAM radio (once I get my license), and other such items to my FJ60. I won't be doing anything super extensive but I would like to be able to understand what I am looking at with a basic knowledge and walk my way through the diagnosis for the most part.

With that said, is there any good websites or books that I can visit, read, watch that will help me out?

The main problem right now is my rear defogger, the negative contact came off the window this fall and I just got around to fixing that. However, I get nothing when I turn it on. Using the multimeter in the Voltage measurement selection I show about 14v when touching the negative and positive wires. When the defogger is off, and I set the multimeter to check continuity and do show 5v continuity so not really sure where/what I am missing.
 
Your de-fogger is a big resistor that heats up with current flow.

Disconnect the +12v and neg terminals and measure resistance in ohms across the de-fogger at the glass. If it is an open circuit you will get a zero reading or beyond range depending on your meter. If this is the case your will need new glass (hence new de-fogger) to fix the problem. Sometimes your can find the break in the circuit on the glass and use a repair kit to fix (paint a conductive material on the glass).

If you get a resistance value, it is probably not the glass/de-fogger but the circuit feeding power to the glass. However, looks like your have already verified voltage at the connectors.

What multi-meter do you have? Measuring continuity will not give you a voltage, rather a resistance in ohms. Make sure your settings on the meter are correct.

Good luck.
 
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the 5 volts is bleed thru...is it a digital VOM? set the meter to ohms, disconnect the power input leads from the window and ohm across the + and - poles at the window. What values do you get...a circuit must have some resistance to be a circuit. zero resistance is a dead short OL or a pegged needle indicate infinante resistance which is an OPEN condition. most circuits will not work in either the shorted or the open conditions. I'm sure the FSM has resistance values for what the defrosters should be...as far as website for introduction to trouble shooting....nothing pops into mind, but cruise youtube a bit with some keyword searches, and I'm sure you'll find something to help illuminate the bulb for you.
 
This is the multimeter that I got (http://www.lowes.com/pd_464295-295-...er&pl=1&currentURL=?Ntt=multimeter&facetInfo=)

I will have to go through the little manual as I really dont know how I should be installing the leads into the meter (assumed that the middle/black/COM was negative and the right/red was positive).

I somewhat figured that it would be a crapshoot to repair the glass as there is old tinting on it and with my dogs back there, who knows what may have happened in the 25+yrs it has been alive. Any idea on how much new glass would cost?
 
Connections:
Black neg probe = com
Red pos probe = V ohm mA

To read DC voltage set dial to 20V=. Straight lines mean DC. Curve lines mean sine wave or AC.
To read resistance set dial 200 ohm for de-fogger.
To read continuity set dial to >| , you will get audible tone.
 
^^^ Thanks that helps a lot... Like I said, I dont even know the basics!!

So here is something funky, when I had the defogger on (after the repair) and set it to continuity and touched the contacts there was no sound or anything (black in com, red in V/ohm/mA) and a 1 showed up on the screen. Is something wrong with my meter?
 
You can't test continuity while it is 'on'. You need to isolate the circuit you are testing so you know the electrical components within the circuit. To measure resistance or continuity of the de-fogger, unplug the power connections and measure resistance of only the defogger without power and without other connections.

Your meter will only sound a audible tone for continuity when the resistance is below a set value, basically a short circuit. This could be a 0.5 ohm or so. If you see a resistance value but do not hear a tone when measuring continuity it is because the circuit has too high a resistance and is not considered a short circuit which defines continuity.
 
Why would he read the instructions? Trying to get his man-card revoked?

I've never found a book on low voltage DC to be complete. The book mentioned above is good, but I've also used this one for reference as well: http://www.amazon.com/Brotherton-pu...Mountain-Paperback/dp/B00ES26078/?tag=ihco-20

It is more advanced, but "Handy Bob's" blog on solar power, while specific to RV solar installs, I've found to be fairly helpful as well. I wouldn't search it out to read until you're mostly comfortable with the contents of either book. And know up front that it is a long, somewhat painful, and repetitive read.
 
If you can make the next meeting and show up a little early I can run you through the basics of DVOM operation and trouble shooting. I also have some basic DC electronics text books you can borrow to learn theory. Let me know and I'll bring the books and my meter next month.
 
Thanks for the info guys... So I got out today and tested the connections again. Will everything off I do get continuity from both ends, on the second dial setting (200v~) I got a consistent reading of 25.3. Since it was actually bright enough out (I normally have mondays off) I was able to inspect the glass and found what could be my issues..

This one you can obviously see the slice that goes across the entire line, Believe this is part of the issue.

Untitled by renofizz, on Flickr

This one is a bit harder to tell but it seems like the conductive material did not really go around the contacts and was thinking that it may not be making full contact.

Untitled by renofizz, on Flickr

I got another batch of the contact cement and did those areas so we will see how that work out.
 
Well no dice, my fix does not seem to have worked so either the contact cement compound is not enough to truly bridge those gaps or I have a break elsewhere that is not allowing the lines to work. This is a bummer as it was working last year prior to the negative side popping off the window.

I have been doing some reading on people trying to repair this and really the concensus is that if it is only the connector popping off the glass then it is a fairly straight forward fix, if not then it is much easier (and less frustrating) to just replace the glass as a whole.
 
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That is what this Permatex stuff I ordered is supposed to be like. None of the places in town had it in stock so the nearest O'Reilly ordered it for me. They will have today so I can hopefully give it a shot this weekend.
 
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