Automotive Electrical Quandry
-
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.
They can be real buggers good luck.
-
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.
Roger Wright wrote:
But in autos, they run the hot (+12V) lead to the device, and switch the ground
I never understood this. Is it a safety thing? Or just a job security thing?
cheers, Chris Maunder The Code Project | Co-founder Microsoft C++ MVP
-
Roger Wright wrote:
But in autos, they run the hot (+12V) lead to the device, and switch the ground
I never understood this. Is it a safety thing? Or just a job security thing?
cheers, Chris Maunder The Code Project | Co-founder Microsoft C++ MVP
-
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.
-
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.
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.
-
Roger Wright wrote:
But in autos, they run the hot (+12V) lead to the device, and switch the ground
I never understood this. Is it a safety thing? Or just a job security thing?
cheers, Chris Maunder The Code Project | Co-founder Microsoft C++ MVP
It's done to save wire. No need to run a ground - just connect the device to a switch that has one side connected to the chassis. It may have made sense when cars cost $500, but it hasn't for a long time.
Will Rogers never met me.
-
It's done to save wire. No need to run a ground - just connect the device to a switch that has one side connected to the chassis. It may have made sense when cars cost $500, but it hasn't for a long time.
Will Rogers never met me.
But why can't you switch it on the live side?
cheers, Chris Maunder The Code Project | Co-founder Microsoft C++ MVP
-
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.
Smart ass... :-D I do my logic design with normal or inverted Boolean operators with equal pleasure, and have no trouble switching negatives, but the manuals refer to the negative as 'ground' so I stick with that convention. After all, in metallic materials the current really does flow from negative to positive, so strictly speaking, the negative is "hot." The wacky part is that dc motors are symmetrical devices - they run equally well in either direction, depending on the polarity of the connection across their armatures. So if it works one way, it ought to work the other. It does, but only with two different switches, connected together in parallel. Here's another clue... When I first connected it, it started to move Up when asked to, then slowed and stopped, almost as if it was running off a capacitor with a little bit of stored charge. It's hard to imagine that two parallel wires in a cable can hold enough static charge to move even a tiny motor, but this is what it's sounding like. Maybe a dirty or loose connection that can trickle charge the cable harness over a long period at low current, but can't sustain a higher current. After 30+ years of designing electrical items, nothing should surprise me, but this one does.
Will Rogers never met me.
-
Did you pop the grommet off near the hinge of the door? Found a few wires through the years had worn unfavorably there. Albeit some grommets are a pain in the @*$ to remove.
Something worth reading, albeit it's invincible!
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.
-
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.
-
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
-
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.
-
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.
-
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.
-
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
-
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.
-
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.
-
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.
-
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.
-
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.
