toobfreak
Tungsten/Glass Member
if you wait till dark and operate the window switch and can watch the overhead roof lights for any dimming, etc., that too can tell you some things.Do the switch test to confirm that the motor misbehaves both from its own door and the drivers.Having recently replaced the mechanism in my own car, I can tell you any mechanic worthy of the title can do this fairly rapidly; it isn't like fitting a 427 into a Sprite!I keep hoping that it is something as simple as a rubber gasket facing the wrong way or lubrication as you say. I plan to keep it as long as it will run. However, if I have to get used to the fact that one of the back windows doesn't work, I can live with that, too, if this repair is going to end up being a huge hairy deal.
It's actually an easy job, usually the hardest part is getting the right nylon fasteners and getting all the panels back into place held tight again. Then there is the other issue: why did the motor die? Did it just go bad or was it forced to fail by an over-current condition because the glides for the window are bad, etc? If you are going to fix this, you want to be sure to fix the CAUSE of the problem, not just the offending part, so that everything works like new again and will stay working well for many years.
It's all speculation until you can:
- Do the switch test to confirm that the motor misbehaves both from its own door and the drivers.
- Assuming the latter, open the door, look in there and assess the problem.
Couldn't I do that just by trying it from my seat and then trying it in back? Then I could tell the mechanic when I bring it in?
Yep. If the motor works normal from the rear door but funky from the driver position, kinda hard to blame the motor. But at least if it acts the same way from either door, it makes it a much safer bet the problem is in the affected door.
Yeah, you'll shock the mechanic by showing him you already used logic and reason to partially diagnose the problem, and maybe suggest to him you aren't an easy pushover. Of course, it would be really nice if you could attach an ammeter to the battery or an inductive one, (you could also put a voltmeter across the battery and watch the terminal voltage) that you can look at the load on the electric as you operate the switch. But maybe if you wait till dark and operate the window switch and can watch the overhead roof lights for any dimming, etc., that too can tell you some things.
- If you're pushing the button and the window doesn't move or hum or anything and the lights appear unaffected, you might have a faulty / open circuit. Terminal voltage doesn't change.
- But if you push the button and the window doesn't move but you hear a hum or see the lights dim, that suggests you have a motor TRYING to work, jammed, stuck, dry, or a short somewhere. Terminal voltage should drop.
I'll do it. Thanks, Toob!
You do understand why that happens!
When you are sitting there with the overheads light on (just open the door), you complete 1 circuit to the battery (R1). Voltage across light bulb basically equals battery voltage (E).
If you operate the window and the lights remain unaffected, that suggests that you closed no other circuit (faulty switch, wire or motor) and the above remained in effect.
But if you operate the window and it doesn't move, etc., but the lights dim, you've opened a parallel circuit to the light. Voltage across light bulb drops dimming the light because now you have a parallel voltage divider circuit.
E: Battery terminal voltage. You only have at best about 13 volts to share amongst the car.
R1: (resistance / load 1) voltage dropped across overhead light.
R2: (resistance / load 2) voltage dropped across window motor circuit. Since these are in parallel to the battery (branch circuits), the voltage available to either will always be the same. If motor is jammed or shorted, R2 will be like a near dead short, current goes way up, battery voltage drops because of Rin, and the overhead lamp acts as a low voltage indicator.
Rin: This is the internal resistance of the battery. All batteries have internal resistance and it goes up with age. When you draw a lot of current from the battery, you drop a significant part of the cell voltage across its own internal resistance, so the terminal voltage drops under load. Your light dims indicating a high load condition that was not there before.
In this case, either the motor is trying to work (held back) or there is a short in the circuit (bad motor, bad wire, or bad switch). If motor acts the same from both doors, probably not a bad switch.
You might want to also locate the fuse for the power windows and try to rotate it or remove and re-insert it just to be sure there is no funky dirty connection there.
Last edited: