Electrical question about the direction of D/C current flow

jaotguy · Aug 12, 2014

also the reason that when someone installs an aftermarket radio (incorrectly ) the auto transmission now shifts funny .. or some other thing stops working ...

and the low signal voltages can be eliminated by mildly corroded wiring ....

crackerjack222 · Aug 12, 2014

All's I knows is that anything electronic has smoke in it. If the smoke gets out, it dies.

Topher265 · Aug 12, 2014

LD1 said:
One question I have (and am surprised of) is that there is no "network" or cat5 cables on cars yet. At least that I am aware of. But again, my experience of "new" stuff ends ~2008. I am sure lots has changed in the last 7 model years

Though someone mentions it below, in the early 2000's manufacturers started networking control modules to reduce weight and "hot" wires. One reason why they don't use a catV cable is they want to use their own specific connectors and wires. Sometimes they only need a couple of wires going to module, not 6.

oldballs said:
Ok, I'm following this tread just because it is interesting. But now my 1999 Crown Vic dome light won't go off, which seems like it might apply here. Where do I look for the problem?
Thanks

oldballs said:
Unlike earlier cars that I owned, there are no door switches that I can find....you know, those metal knobs that spring out when the door is opened and are pushed in when the door is closed. I can't find anything that controls the door(s).

Your door has switches in the latch and maybe in the handle (depends if you have keyless entry). These feed into a solid-state (*ahem* "computer") "Lighting Control Module". Which light is your "dome" light? Do you mean the light overhead with a map light on each side and the main light in the center? Make sure the map lights aren't clicked "on".

Do any other lights stay on? Or do any other lights/switches not work? I'll be glad to help you track down what's causing it.

Jkott said:
Ever heard of Canbus? My 2006 GM is controlled by a data network. For example just a power and data line go to the passenger door to control the power windows, locks, etc. they eliminated a lot of weight when they eliminated many of hot power leads and went to various control modules.

Of course most old school mechanics have no idea how data communication works or how to troubleshoot it. That's why many people have such issues with electrical gremlins in modern vehicles. Eventually training will catch up and more mechanics will actually be able to fix the electrical problems as reliably as the mechanical ones.

Excellent post. Very very true...successfully repairing modern cars requires two simultaneous trains of thought. One needs to think of the mechanical systems at play as well as analyze the electrical controls. There is almost nothing that operates on a modern car that is free from the electrical system. I find it's sort of like needing an IT person in your brain as well as the traditional mechanic.

In fact, these two systems at play simultaneously is the main reason why I love working on cars. I've always loved the electrical diagnosis/repair side of things...it pays better when you're very good at it

.

DarkBlack · Aug 12, 2014

bcp said:
Flow on the surface only?

If so, an insulated piece of copper tubing (nearly twice the surface) would carry almost twice as much as a solid wire of the same diameter?

Bruce

If DC only flowed on the surface, your example would be correct.

DarkBlack · Aug 12, 2014

skyhook said:
Yep, thats why when you see corroded "green" cables, on the outside, when you split the cable open,
you know it's time for new cables "or' wire".
Electrons flow around the outer cable, believe it.

LOL, I'm no "Master Electrician", but i do have my masters in Electronics,
Think about this for a second.....
when you pull back a connector on your tractor and one of them "fall of" due to corrosion,
you strip back the wire to reconnect it only to find the wire is all green from humidity etc,
yet, when you cut that wire in half, it's nice and copper clean on the inside,
now ask yourself, "why" didn't it conduct.

Skyhook.....DC flows through the entire conductor. You'll just have to get used to it. Maybe physics changed since your masters.

oldballs · Aug 12, 2014

Well thanks, Topher. As mentioned earlier the "switch" could be in the latch. So I figured out which door was the culprit and "fiddled" with the latch and so far, everything is okay. But I expect that the problem will probably return. The dome light and the feet courtesy lights are the ones that had the problem. ...but I shouldn't highjack this post. It was nice to hear the "consensus" that electricity flow from the neg to the pos, but how that will effect my day, I'm not sure.

CobyRupert · Aug 12, 2014

oldballs said:
It was nice to hear the "consensus" that electricity flow from the neg to the pos, but how that will effect my day, I'm not sure.

.....The more positive you are, the greater chance you'll get hit by lightning. :confused3: (It's never the negative people that you wish would)

Threepoint · Aug 12, 2014

oldballs said:
Well thanks, Topher. As mentioned earlier the "switch" could be in the latch. So I figured out which door was the culprit and "fiddled" with the latch and so far, everything is okay. But I expect that the problem will probably return. The dome light and the feet courtesy lights are the ones that had the problem. ...but I shouldn't highjack this post. It was nice to hear the "consensus" that electricity flow from the neg to the pos, but how that will effect my day, I'm not sure.

Late to this thread, as I see you've found the problem. The OP's a nice guy; I doubt he minded your hijack at all. :laughing:

This is a known issue with some Ford products of that age, which I learned researching the same symptoms on my '99 Expedition several months ago. Dome light doesn't go off after opening and closing one of the doors. The driver's side door is usually the offender. Strange but true, the three-minute fix is to spray a couple quick shots of WD-40 into the door latch mechanism using the red straw to direct the spray. :thumbsup: If the problem returns in a few months (and it may not), repeat the treatment. The dealership's solution would be to replace the door latch, a very spendy proposition. Good luck.