MrLexse

Okay, the driver's window won't go down (or up), so I replace the switch with a new one and cross check the new switch on the passenger side window, which operates correctly. The switch works.
So far so good.
I pull off the interior panel on the drivers door. I jump directly to the motor terminals with test wires (directly from the battery). The motor doesn't work.
Ahah. Not too bad.
I take out the motor, take it apart, thoroughly clean and re-lube it and try it again - it works perfectly. I reinstall the motor, jump it from the battery, and the window is going up and down like new.
Sounds like I've got it.
I test the harness clip terminals with a voltmeter (to ground) as the switch is depressed (either up or down) and the corresponding harness terminal shows 12+ v.. I clip it onto the motor.
Nothing.
When powering (+) either motor terminal and grounding (-) the other terminal, the motor will run. When the harness clip is attached, it can alternately feed (+) either terminal, but it seems to be missing the ground properties (-) that I get with the test leads. If I run a voltmeter across the harness clip terminals when either is energized, I get nothing.
What gives?

JP Rodkey

You don't want to measure volts to ground at the harness (one lead on the harness, the other to car body) because both poles are switched. You want to put both leads on the harness connectors and see if you get +12V when operating the window switch, then -12V when the switch is pushed in the opposite direction. Based on what you wrote, I'm betting you won't get good results.

Double check wiring of your new switch. If that proves okay, check continuity between window motor connector lead to the window switch plug at the firewall. A common problem is wire break where the harness goes between the door and the A pillar due to years of bending - especially driver side.

MrLexse

The switch works when connected to the other window, so I think it's good. A voltmeter across the harness terminals (when switched on) shows no current at all, not the +12v/-12V I am looking for. Wouldn't the harness terminals, each producing 12v when switched on and grounded, show that the wires themselves, were sound?

JFCIII

Lex,

Which car?

JP Rodkey

They need to show 12V between them when the switch is operated - not each individual lead to body ground. Check continuity for each wire from lead back to the plug where the switch leads are connected. You're describing a broken circuit somewhere between the switch and the motor. Likely one of the wires is broken, not allowing a complete circuit path for either 'up' or 'down'.

JFCIII

To add to JP.

4 wire switch. 1 terminal is 12v from relay, 1 terminal is ground, the other two alternate the power and ground supply to the motor. If you can run the motor by using 12v and ground at the motor and that won't work at the two supply wires at the switch the you have a broken wire some where and which one.

Ohm the wires between the switch and motor and see if you have an open circut.

I have seen this and some times the window will only work with the door closed because it closes the break.

If this is your '94 can't you control the windows with the key? This makes more complicated.

MrLexse

John,
On the 94 (like all GTS's), if you turn and hold the key, it will close all windows and the sunroof sequentially, then lock both doors and set the alarm. Pretty cool.
But I digress, it's my 87, and I think it's sinking in (note avatar).
If I get a chance, I'll grab my ohmeter and teach that shark an electrical lesson it will never forget!
(I'll let you know who wins). Thanks all.

Shark Attack

Your avatar is great... below is your problem

Alan

It actually doesn't really make much difference - either test wil work.

before you dive into the doors I always recommend pulling the switch out and testing the rear terminals - do it now...

Red & Brown are power from the relay & ground check these have ~12v across them - (If not its a fuse/relay or connection problem) also check these when operating the switch in both direction - do you maintain ~12v - if not you have a relay contact or connection problem between the switch and relay.

If this test is good - test the voltage between the switch output pair - you should have the same ~12 - positive in one switch direction and negative in the other.

OR you can measure each terminal to ground and in each direction 1 should be at ~12v and the other at ~0v - when the direction changes the voltages on the pins should swap.

If these are <<12v or >>0v you most likely have a switch contact problem. if these are good and the motor doesn't run - its either broken (OC probably) or there is a break in the wiring to the motor... this is the time to open up the door and test the motor connections directly - preferably with he motor still connected. If the motor has to be disconnected - at least test the wire voltages - then test applying battery voltage directly to the motor to see if it works.

There are cases where contact resistance will make it seem a connection is good with no load (e.g. here no motor) - yet when the motor is connected the voltage will collapse...

Alan

JFCIII

Very well put Allen. I have gotten so use to using a Power Probe it is hard to put all that into words.

John Struthers

Well! Hot Damn!
This should also work for that 'new' switch I procured for the sunroof.
I had to swap connector blocks from the old to new switch harness...nada!
Direct juiced the motor...works fine. Lazy me, I've been running without the panel and using the
Porsche supplied manual crank.
Back to work...thanks all.

wg928

wayne has been/is an electrician for many many years if you need him he will gladly help you for free call him/me 917-202-5324. he/I live 20min from your garageand love opportunities to come out and play with 928's

MrLexse

Thank you Wayne. Let's see... in 5 minutes you diagnosed and repaired the drivers window, and found a faulty fuse which looked to be good, which in turn got my interior lights working again. That was my next project - now what.