syoo8

Hi everyone,

I'm swapping out my window motor for a good used unit from Tom at 928 International. In the meantime, a couple of days ago I cleaned all of the ground points on my '87 S4, the jump post, and the ground strap. I cleaned the CE panel extremely thoroughly 2 years ago. I cleaned the terminals of relay VI (window lift relay) this afternoon.

I'm measuring 12.8 volts at the jump post, 12.8 volts at the top of the CE panel, and yet only 12.3 volts at the connector that plugs into the window motor.

Do any of you have ideas about why the car is losing about a half a volt?

Speedtoys

All of that goes up thru the window switch too, including ground. Is EVERY contact in that path pure and clean?

Mrmerlin

put deoxit into the window switch contacts use deoxit 100

MainePorsche

From it's source Mr. Electron doesn't lose much and ends up with 12.8 when he arrives at the CE panel. Upon entering this mileu he goes through very small wires and a relay, hops over the high resistance of of the fuse substance to then again enter small wires until he reaches the terminals at the window motor. Mr Electron courses over trails where resistance is variable, but certainly not at nil. Deoxit as Stan instructs and worry not. There is really not much to do about natural losses.

syoo8

I forgot to mention that the window switches are brand-new, Stan. Thank all three of you for your replies!

Tomkat80222

Does the window go up and down as you want? If so

docmirror

You power windows derive their 12V through relay Vi 'power window regulator'.

Proceed:

1. Remove the leads to the window motor.
2. Start the car, let it idle.
3. Put red meter lead on one of the leads of the motor.
4. Press and hold the window switch. Check for ~14VDC. Let voltage stabilize. If you get nothing, press the switch the other way. Record voltage, this is your reference voltage.
5. Move red meter lead back to pin 3(red) of window switch, hold down button and record voltage. Compare to step 4.
6. Locate CE pin G23. Move red meter lead to G23, record voltage, compare to step 4.
7. Locate fuse 15, remove it. Move meter lead to fuse 15 source pin, record and compare voltage to step 4. Replace fuse 15.
8. Remove relay VI. Move red meter lead to pins 30, then 85 and record voltage. Replace relay VI.
9. Insert jumper from pin 87 to pin 85 in relay VI socket, move meter to pin 87 of socket and record voltage.

To better see voltage drops it helps to have a load on the system. If you can connect the motor and make the tests, you may see a greater drop due to the current flow. Look for the greatest voltage drop along the test path. Keep your ground reference in the same location for all tests. Report results.

syoo8

Hi doc,

Thank you so much for your thorough, detailed (as usual) procedure!

Step 4: 13.80 volts in both directions
Step 5: 13.78 volts
Step 6: 13.86 volts
Step 7: 13.78 volts
Step 8: .01 volt for pin 30, .09 volt for pin 85. I tried to get different results for about 15 minutes and was unsuccessful-- I'm assuming I did something wrong here.
Step 9: .01 volt jumping pin 87 to 85 and measuring at pin 87.

The window is moving better than it used to, but I think that's because I am using a replacement motor from 928 Int'l.

Thanks again for your help doc!

Alan

My answer is a little different. I think you have a measurement problem.

Assuming we are talking key out and motor not operating I suspect there is less actual difference than you think under the same conditions.

The same conditions are the key. You need to use the same ground for all measurements. And you need the same operating conditions - the variable here may be the interior lights. Ideally you need the interior lights off in all cases - since with the key out they are typically by far the largest consumer.

With the lights off you have virtually no current being consumed by the car and under these conditions the voltage will not vary with resistance in the circuit. V=I*R so the voltage dropped across a circuit resistance will be zero if the current is zero. Now the battery is also interesting - at its high terminal charging voltage ~12.8v) its voltage is very susceptible to small load currents and may never fully recover to the max 12.8v value (a temporal effect).

So: Repeat the measurements with a common ground point (battery -ve), ensure the interior lights stay off by taping the door switch and removing the Brown/wire wire for the hatch switch. Then measure these in reverse - start with the windows, then the jump post then the battery.

Another option measure battery voltage and window voltage at the same time with 2 meters under various load conditions - do verify the meters read the same on either voltage as a double check.

Alan

docmirror

Hmmm, I wonder what happened at 8 and 9? I'll have to review.

Anyway, it appears you have no major parasitic losses in-situ. If you wish to proceed further, we can go through the ground ref side of the testing. However, I believe you've done the ground cleaning process thoroughly, so it's unlikely that there are going to be gains made on the ground plane side. It is important to note that as you make voltage tests, that the ground lead of the meter always remain in the same place. If you moved the ground in your initial measurements, let me know, and I'll develop a ground ref test process.

'Ground loops' are often the bane of analog test processes. I once got a sensitive meter and tested the front ground point where the headlight connects and the battery - lead, and saw ~.65 volts with the headlights on. It's possible there's a ground loop, but we won't know without running the ground side.

Glad to hear it's working better with the new motor.

syoo8

Thank you docmirror for all of your help.

Alan- thank you for replying. Yes, my measurements were not with the same grounds in the original post, and were made with the engine off. As per docmirror's instructions, I connected the voltmeter to the battery ground strap and made measurements that way.

Alan

The most important thing to get here is that the battery is not a fixed voltage - it varies with load and state of charge and even just time (even a few seconds under some circumstances). Somewhat true of the alternator too.

When you have no load (motor is not running) you have no voltage drops across resistance in the path due to that load - any drop is due to another major load OR more likely just the effect you are having on the battery voltage itself.

You can spend a lot of time chasing your tail here.

Alan

drooman

I think you should rename the thread: 928 electrics SUCCESS - ONLY losing .5v