Automotive Electrical Quandry
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But why can't you switch it on the live side?
cheers, Chris Maunder The Code Project | Co-founder Microsoft C++ MVP
Ask an automotive engineer; I just design reliable things. I would have thought that by now, with integrated, serial-bus devices so cheap, they would include one in every device in the car, connected by a three-wire CAN bus cable - one +12, one -12, and one Comm line. I can't believe that cost is an issue anymore, and diagnostics would be far more reliable and informative.
Will Rogers never met me.
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Ask an automotive engineer; I just design reliable things. I would have thought that by now, with integrated, serial-bus devices so cheap, they would include one in every device in the car, connected by a three-wire CAN bus cable - one +12, one -12, and one Comm line. I can't believe that cost is an issue anymore, and diagnostics would be far more reliable and informative.
Will Rogers never met me.
Maybe you're just used to American cars Oooh! Cheap shot!
cheers, Chris Maunder The Code Project | Co-founder Microsoft C++ MVP
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A week ago my passenger side electric window stopped working. I tested everything I could reach and found nothing wrong, so surmised that the motor was a goner. I ordered a new one and popped it in place; no joy. So I tossed aside the repair manual and started using my brain instead. I found that, with the cable to the motor disconnected, all voltages were as they should be, but with the motor plugged in, the motor rolled down correctly, but the voltage dropped to 0 when switched to the Up direction. Great... there's a wiring problem somewhere under the dash. Since that window can be operated from either side of the truck, I tried checking it from the driver side switch. From there, it works fine in the Up direction but fails when I try the Down position on the switch. Crikey! The two switches are wired in parallel - how can this happen? I hate automotive engineers; they do everything backward. Any normal circuit leaves one side of a device grounded and switches the hot lead. But in autos, they run the hot (+12V) lead to the device, and switch the ground. That leads to some interesting side effects when a wiring fault occurs, and makes life miserable for anyone trying to diagnose a problem. This is going to take a while to figure out, and in the meantime, I have a 3/8" ratchet taped inside the door, holding the window mechanism in the Up position until I can find the fault. Grrr...:mad:
Will Rogers never met me.
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That was the first thing I suspected, when I only knew about the one switch not working. But I haven't found anything abraded yet, though I'm still looking. "My Kingdom, my Kingdom for a Time Domain Reflectometer!" That would make short work of this adventure...
Will Rogers never met me.
Roger Wright wrote:
a Time Domain Reflectometer would make short work of this adventure...
Not so sure! A TDR could tell you it's 4.5 ft from this end, but where the h*ll is that? Even without a TDR, I could tell you the problem is within 6 ft of the steering wheel. ;P Cheers, Peter
Software rusts. Simon Stephenson, ca 1994.
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Probably a bad ground strap from the door to the car body. ie: Flip the switch one way & it works because it sees a ground through the other switch in the other door. Flip the switch the other way & must use the local ground but can't. -- Ian
That's a thought... I haven't really investigated it yet. But, from the schematic and observation, there's no local ground on the passenger side - the two motor leads go across the cab to the driver side switch, and from there to a common ground connection. I pulled the driver side switch module tonight for testing this, and unlike the other side, this one is filthy with dust. Tomorrow night I'll tear it apart - not intended by the manufacturer, but easy to do - and give it a good cleaning with contact cleaner. There could be a high resistance connection in there caused by dust build-up.
Will Rogers never met me.
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Roger Wright wrote:
I hate automotive engineers; they do everything backward. Any normal circuit leaves one side of a device grounded and switches the hot lead. But in autos, they run the hot (+12V) lead to the device, and switch the ground.
Your statement makes little sense to me, as everything is relative, as usual. Imagine you rename the wires, from now on what used to be +12V will be called GROUND. And what used to be ground will be called POWER (and holds -12V with respect to the new GROUND). All of a sudden you are switching the "hot side" of things, like you prefer. All without rearranging any of the wires. Now go fix the wiring fault your car is having. :)
Luc Pattyn [My Articles] Nil Volentibus Arduum
Fed up by FireFox memory leaks I switched to Opera and now CP doesn't perform its paste magic, so links will not be offered. Sorry.
Not to mention that circuit designers keep drawing the current going from positive to negative...
cheers, Chris Maunder The Code Project | Co-founder Microsoft C++ MVP
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Not to mention that circuit designers keep drawing the current going from positive to negative...
cheers, Chris Maunder The Code Project | Co-founder Microsoft C++ MVP
It really does help to have some convention, even if it's not the physically correct one. And maybe it was predestined, as after a hundred years or so of drawing it wrong, Russell Ohl finally corrected all the drawings by discovering the p-n semiconductor junction, through which the current flow really is from positive to negative. Now that we rely on his discovery for almost everything, we can easily discount the importance of all those old-fashioned metal connections between the things that do all the work.
Will Rogers never met me.
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Maybe you're just used to American cars Oooh! Cheap shot!
cheers, Chris Maunder The Code Project | Co-founder Microsoft C++ MVP
Go ahead - take your shot. :-D For autos, it's well deserved by American industry. But my main power feed, a 69kV line from Davis Dam, has been standing and functioning since 1943. I've designed its replacement, which I'll start building in a couple of weeks, and owing to improvements in materials and construction methods, it will very likely last twice as long. ;P Of course, if it only lasts long enough for me to be safely retired, I'll be content; I don't live on the reservation it serves.
Will Rogers never met me.
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Roger Wright wrote:
a Time Domain Reflectometer would make short work of this adventure...
Not so sure! A TDR could tell you it's 4.5 ft from this end, but where the h*ll is that? Even without a TDR, I could tell you the problem is within 6 ft of the steering wheel. ;P Cheers, Peter
Software rusts. Simon Stephenson, ca 1994.
So, that's a 25% improvement, and will probably save me an hour of spelunking under the dash. In all likelihood, it's a connector problem; over 80% of electrical problems turn out to be connectors. There are just a couple to check, and as I mentioned below, my prime suspect is the switch module in the driver door, since it's covered with dust. The stuff is everywhere here - if I dust the house and seal the windows and doors with tape, I'll still find a millimeter or so of the stuff on every surface within a couple of days. It's extremely fine, river bottom clay silt that forms a colloid when suspended in air and permeates everything. Cats don't have a problem with hairballs here; they cough up adobe bricks. I strongly doubt that the usually efficient Japanese engineers who designed this truck could imagine the climatic conditions their product has to deal with in Bullhead City. No manufacturer could without the help of a bad batch of Prozac.
Will Rogers never met me.
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I believe it relates to having less draw on the Electrical system. :doh:
Something worth reading, albeit it's invincible!
I'd love to see a proof of that theory! :laugh:
Will Rogers never met me.
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They can be real buggers good luck.
There's one shop in Bullhead City that does nothing but fix electrical problems. His yard is always full of vehicles, and some of them never leave. I'm thinking that this could be a good retirement income opportunity when he gets tired of doing it. There's definitely a need, and I don't foresee the market getting smaller.
Will Rogers never met me.
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Don't ever buy a 2000ish Jetta unless you're a masochist. I had to go to the dealer because of my lack of knowledge for: driver side power window (twice), passenger side power window, windshield whippers, and after many trials and errors with the key programming, the whole instrument cluster. On second thought I propably would be just as pissed if I had the knowledge. And the service was so bad for my lemon, I change my recommendation to don't ever buy a VW. Rant over.
I'm certainly a masochist, having been in love with a woman for fifteen years who still wants to be "just friends." But there's a limit to the amount of pain I'm willing to endure, and buying a VW isn't on my list of things to do - ever. Unless, of course, it's a vintage 1969 VW microbus with a pop-up roof; that I could deal with... :-D
Will Rogers never met me.
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I feel your pain and pray to the gods that your car is not a BMW the electrics in them are the worst !!
According to the ads, and consistent with the pricing, BMWs never break. Are you suggesting that their advertising is somehow less than entirely accurate?
Will Rogers never met me.
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Probably a bad ground strap from the door to the car body. ie: Flip the switch one way & it works because it sees a ground through the other switch in the other door. Flip the switch the other way & must use the local ground but can't. -- Ian
I have discovered exactly that issue with one of the brake lights in Booger Mobile (see link below)... When the headlights are off, the brake lights both work fine. When the headlights are on, one of the brake lights doesn't work (but the tail light continues to work). After diagnosis, it's exactly as you described above. When the headlights are off, it's earthing out the taillight wire, but when the headlights are on, the taillight wire has current flowing through it, so it can't earth there any longer... It was a Eureka moment for me when I discovered that... now to fix it before this year's esCarpade!!
Silence is golden... but duct tape is silver!! Booger Mobile - My bright green 1964 Ford Falcon - check out the blog here!! | If you feel generous - make a donation to Camp Quality!!
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There's one shop in Bullhead City that does nothing but fix electrical problems. His yard is always full of vehicles, and some of them never leave. I'm thinking that this could be a good retirement income opportunity when he gets tired of doing it. There's definitely a need, and I don't foresee the market getting smaller.
Will Rogers never met me.
Agreed! A lot of people I know, including me have electrical problems. If you had the right tools and a big ole shade tree you could retire with more money than ole Billy Bob Gates. :)
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A week ago my passenger side electric window stopped working. I tested everything I could reach and found nothing wrong, so surmised that the motor was a goner. I ordered a new one and popped it in place; no joy. So I tossed aside the repair manual and started using my brain instead. I found that, with the cable to the motor disconnected, all voltages were as they should be, but with the motor plugged in, the motor rolled down correctly, but the voltage dropped to 0 when switched to the Up direction. Great... there's a wiring problem somewhere under the dash. Since that window can be operated from either side of the truck, I tried checking it from the driver side switch. From there, it works fine in the Up direction but fails when I try the Down position on the switch. Crikey! The two switches are wired in parallel - how can this happen? I hate automotive engineers; they do everything backward. Any normal circuit leaves one side of a device grounded and switches the hot lead. But in autos, they run the hot (+12V) lead to the device, and switch the ground. That leads to some interesting side effects when a wiring fault occurs, and makes life miserable for anyone trying to diagnose a problem. This is going to take a while to figure out, and in the meantime, I have a 3/8" ratchet taped inside the door, holding the window mechanism in the Up position until I can find the fault. Grrr...:mad:
Will Rogers never met me.
There should be a (or maybe two) (micro-)switches that stops the motor when the window is in either "end position", fully up or fully down. Which prevents the motor from burning if you keep holding the switch. Maybe you should start looking there? My 5 cents...
Alcohol. The cause of, and the solution to, all of life's problems - Homer Simpson
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I have discovered exactly that issue with one of the brake lights in Booger Mobile (see link below)... When the headlights are off, the brake lights both work fine. When the headlights are on, one of the brake lights doesn't work (but the tail light continues to work). After diagnosis, it's exactly as you described above. When the headlights are off, it's earthing out the taillight wire, but when the headlights are on, the taillight wire has current flowing through it, so it can't earth there any longer... It was a Eureka moment for me when I discovered that... now to fix it before this year's esCarpade!!
Silence is golden... but duct tape is silver!! Booger Mobile - My bright green 1964 Ford Falcon - check out the blog here!! | If you feel generous - make a donation to Camp Quality!!
Though it shouldn't work that way, your diagnosis is right on, given the information available. Automotive electrical wiring depends on a good frame ground, and it just ain't so - steel isn't a good conductor. Try grounding the headlights with a separate copper wire between the lights to ground, giving them their own dedicated ground. They draw a lot of current, and if your theory is right, the brake lights will work fine after the rewiring. It's said that electricity always finds the shortest path to ground. That's a lie. Electricity always finds every path to ground, it just divides the current among the paths available to allow the most current to flow along the path with the least resistance. Providing a low resistance path for the headlights will give the brake lights a little spare capacity on the frame ground. Of course, if this doesn't work, your theory is wrong and there's an entirely different reason for this behavior. That's always a possibility, but it's worth trying to eliminate potential problems that are easily isolated. The trouble is that there are so many possible causes; this will eliminate one, but there may be others. Still, it's a good start.
Will Rogers never met me.
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Though it shouldn't work that way, your diagnosis is right on, given the information available. Automotive electrical wiring depends on a good frame ground, and it just ain't so - steel isn't a good conductor. Try grounding the headlights with a separate copper wire between the lights to ground, giving them their own dedicated ground. They draw a lot of current, and if your theory is right, the brake lights will work fine after the rewiring. It's said that electricity always finds the shortest path to ground. That's a lie. Electricity always finds every path to ground, it just divides the current among the paths available to allow the most current to flow along the path with the least resistance. Providing a low resistance path for the headlights will give the brake lights a little spare capacity on the frame ground. Of course, if this doesn't work, your theory is wrong and there's an entirely different reason for this behavior. That's always a possibility, but it's worth trying to eliminate potential problems that are easily isolated. The trouble is that there are so many possible causes; this will eliminate one, but there may be others. Still, it's a good start.
Will Rogers never met me.
I gave it a temporary earth to the frame from the offending tail light, and it resolved it... I just need to make a permanent one! I actually have a couple of earth straps on BM (the factory one to the engine and an additional one to the chassis) to provide a healthier earth for all the flashing lights and whizz-bangs... Made a huge difference!!
Silence is golden... but duct tape is silver!! Booger Mobile - My bright green 1964 Ford Falcon - check out the blog here!! | If you feel generous - make a donation to Camp Quality!!
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There should be a (or maybe two) (micro-)switches that stops the motor when the window is in either "end position", fully up or fully down. Which prevents the motor from burning if you keep holding the switch. Maybe you should start looking there? My 5 cents...
Alcohol. The cause of, and the solution to, all of life's problems - Homer Simpson
Good thought, and I would design the circuit that way, but Nissan didn't; there are no limit switches or overcurrent detectors in the circuit. There are a couple of fuses, but they would blow if the circuit for either direction of movement was overloaded, but they haven't. That, at least, tells me that I'm not dealing with a short circuit, which would quickly blow a fuse.
Will Rogers never met me.
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According to the ads, and consistent with the pricing, BMWs never break. Are you suggesting that their advertising is somehow less than entirely accurate?
Will Rogers never met me.
