Power Window Problem - PeachParts Mercedes-Benz Forum

RCH89190E · #1 08-28-2008, 12:31 PM

Posted a few days ago about replacing the passenger front window motor. Jump tested it in the door and it wouldn't budge. Ordered a replacement motor and after I removed the old one decided just for grins to shoot some juice to it. Well, the old one came back to life and worked great. Re-installed and it worked perfect using a 12volt power supply jumper. Hooked up the console switch and using the cars power switch...the thing is slow and has to be helped up with a hand against it. Doubted myself and I checked again by hitting it with the power supply juice. (works perfect with the pwr supply), but sluggish with the console switch. Is there some type of voltage regulator that controls the power from the cars voltage to the windows? It seems it just isn't getting the power it needs. Any imput would be appreciated.

Dee8go · #2 08-28-2008, 12:36 PM

Could dirty contacts in the switch cause this?

mpolli · #3 08-28-2008, 02:22 PM

If you say what car you are working on you might get more answers. They are not all wired the same.

G-Benz · #4 08-28-2008, 02:34 PM

I assume from his tag...an 89 190E...

RCH89190E · #5 08-28-2008, 08:28 PM

Sorry, it's an 89 MB 190 E. Don't think it's the switch, just replaced it. I put a voltage meter on the contact with the switch wire attached and it shows a 12 volt load when the power is on and shows the same when the switch is pushed. I dabbed a little all purpose grease in the regulator tracks and that didn't help. It still needs help with a hand to open and close. ???????????? Tomorrow I am going to try running a jump wire from the console switch to the hot lead of the window motor switch on the door. This should bypass any "regulator" that is lowering the voltage.

tyl604 · #6 08-28-2008, 08:40 PM

Could a bare wire be draining some of your power when you hit the switch and allowing only some of the juice to go to the motor? Guess another way to state it is - can you test the juice you are getting through the wire just before it attaches to the motor?

mpolli · #7 08-28-2008, 09:43 PM

Quote:

Originally Posted by RCH89190E

Sorry, it's an 89 MB 190 E. Don't think it's the switch, just replaced it. I put a voltage meter on the contact with the switch wire attached and it shows a 12 volt load when the power is on and shows the same when the switch is pushed. I dabbed a little all purpose grease in the regulator tracks and that didn't help. It still needs help with a hand to open and close. ???????????? Tomorrow I am going to try running a jump wire from the console switch to the hot lead of the window motor switch on the door. This should bypass any "regulator" that is lowering the voltage.

I think what you are saying is you put your volt meter probes across the switch contacts and read 12V whether the switch was pushed or not? Is that correct? Or did you do a different test? If that is what you did then that shows your switch is bad. One test you can do is jumper over the switch with a piece of wire. If the window works then it shows the switch is bad. A schematic would be nice however...

RCH89190E · #8 08-29-2008, 04:39 AM

I plan to jump a wire from the switch to the wire at the motor. I tested the wires at the motor using a 12 volt source, and the unit works up and down with normal speed. I will test the lead to the console switch and then after the switch. Will let you know what happens.

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280EZRider · #9 08-29-2008, 04:43 PM

MBZ uses a common relay for all windows. Have you checked it?

RCH89190E · #10 08-30-2008, 12:09 PM

Saturday morning update:

Ok, bypassed the switch at the console with jumper wires going from the hot lead and ground (on the female switch wiring plug) directly to the motor wires (blk/wh, gr/yellow). I have current but the motor will hardly move up or down. Note* this is the same motor in the door, that when using external power from a 13.8 power supply, works fine. There is no binding of the window glass in the tracks to cause any kind of hanging up.
It appears that the internal wiring just can't produce the juice needed to operate the window. The drivers side has no problem. I even connected an extra motor to the passenger side wiring and the same thing.

I also ran two single wires from the battery pos and neg terminals to the motor wires and the window operates fine. It is definatly not the motor. It appears that somewhere, somehowm the voltage is being dropped in the wiring harness at the console. Would the window switch relay under the hood be a possible culprit?

Peter Guenther · #11 08-30-2008, 01:40 PM

I would think the switch reverses the polarity to the motor for up and down, could the wires in the door hinge have broken down. check the voltages at the switch with the button pushed

RCH89190E · #12 08-30-2008, 02:55 PM

Looking at the schematic from a 88 shop manual, (which appears to be the same as the 89, wiring colors are the same) It looks like the rear window switch and motor are connected to the same harness by a common ground. I am going to disconnect the switch on the rear door and check that. by the way, the motor in the rear passenger door is dead as far as I know. I am wondering if it might have a constant electrical load on it causing my problems. Don't know what else to trouble shoot other than the relay, which seems to be fine, because the drivers side front and rear work fine. I haven't figured out if there might be a relay for each side yet.

mpolli · #13 08-30-2008, 06:26 PM

If you have a scematic then there is some hope. You should be able to see if a relay is involved or not.

Peter is correct. You should measure the voltage at the switch:

First, put the red lead of the meter on the incoming power contact of the switch and put the black lead on a known good ground. Measure the voltage with the switch off. It should be at least above 12V. (It should be whatever the battery voltage reads).

Now push the switch and see if the voltage drops and how much. Normally it shouldn't drop much. maybe 1/2 volt. If you see a larger drop then you need to trace the path from the battery, through the fuse, connectors, relay if any, etc. If the voltage doesn't drop then you need to look at the ground side of the circuit. If I had the schematic I could hopefully give better advice. I remember on my 86 Supra, the passenger window had a switch on both doors so the driver could control it also. And the switches were wired together in kind of an odd way. I had to study the schematic a while to figure it out. In that case the swicth on the drivers door needed repair.

RCH89190E · #14 08-31-2008, 08:41 AM

I'm leaning more to a bad window relay in the fuse box. That might be the answer. Will pull today, clean, and put it on the tester. This might explain why the passenger side window is getting lower voltage that the driver side. After jumping the wire from the console window switch plugs to the motor and getting low voltage, It's not the wiring from the console to the door or the switch.

RCH89190E · #15 09-03-2008, 10:06 AM

Update:

Tested the window motor with both power supply and direct current from the car battery at the motor wiring at the door.(Disconnected from the console wiring harness), motor operates fine, window goes up and down with ease at normal speed. Jumped a set of wires from the driver door window wiring to the passenger window motor wiring and it works with ease. Tested with the left driver console switch connected and it works fine. Hooked everything back up and the passenger side window connected to the passenger console switch and it won't go up and down without hand help. Bypassed the console switch to the window motor and it won't work well. Apparently the right side wiring is the culprit from the relay to the switch. Check the relay under the hood and it is fine. Switches check out fine. I think I'm just going to figure a way to bypass the harness and run a new source of current to the switch. Also, disconnected the rear door motor, thinking that was maybe drawing on the voltage. Did, and no change.