Low volts on driver side window

[GJR]

Hi all,

I’m looking for some advice on an electric window power supply fault.

My driver side window recently stopped half way up. I managed to fully raise the window using a separate 12V supply, so I know the motor is okay. The passenger window is operating fine showing 12V at the door when the window switch is operated. The driver side supply to the door is just 2V which explains why the motor failed to operate.

Does anyone have experience of a similar issue? What would be the likely culprit for the voltage drop and what should I check next?

Appreciate any advIce.

[phillpot]

GJR said:

Does anyone have experience of a similar issue? What would be the likely culprit for the voltage drop and what should I check next?

The switch? try swapping side to side

[GJR]

Thanks Mike, I changed switches around and they are okay. Driver side switch operates the passenger window, passenger switch makes no difference to the driver window.

Is there likely to be another fuse or relay in the wiring? I’ve had the car since it was a year old so I know the wiring should be as it left the factory. It’s a “97 500 if that makes a difference to the wiring layout?

[phillpot]

To give a huge volt drop like that it's more likely to be a very loose and/or corroded connection somewhere I'd have thought?


Think there's a multiplug lying in the bottom of the door, prone to corrosion.

[rigga]

High resistance somewhere is causing the voltage drop, as suggested its probably a lot of verdigris in a block connection, need to trace back through to find where it is.

[GJR]

Mike, Martin, thanks for the responses. I’ll investigate at the weekend.

[Penelope Stopit]

This might be a good time to carry out the 2 relay per door polarity reverser mod

[phillpot]

Penelope Stopit said:

This might be a good time to carry out the 2 relay per door polarity reverser mod

Have you done this on your car, any pictures?

[GJR]

Hi All,

I've been able to do a little more investigating this afternoon. Interestingly, the first thing I did was try and open the window and it worked first time. I checked the power to the window and this is now back to 12V. The car has not been used over the week, but has been on my drive way with a trickle charger connected.

I checked the wiring harness in the door and it seems to be in good condition with no damaged wires and all used connectors looking okay with no corrosion. I did, however, notice an unused connector shown in the image below with the (??) next to it. Any Idea what that connector is for?



The only other branches off the main harness were to the mirror, and to a relay (image below) which I'm guessing is related to the mirrors? It wasn't possible to see the condition of the wires going into the back of the relay socket, but the relay itself was not corroded and looked to be in good condition. Would that relay circuit have any influence over the window power?

On the cabin side the harness goes up to the dash and I assume from there the connections are earth, fuse box etc?

With the drop to 2V at the window power supply, and recovery to 12V over a few days, could this be an earthing problem? If so which earthing point would it be?



Thanks for all the comments so far.

[David Beer]

phillpot said:

Have you done this on your car, any pictures?

With this mod the windows go up twice as fast !

[phillpot]

GJR said:

Hi All,

I did, however, notice an unused connector shown in the image below with the (??) next to it. Any Idea what that connector is for?

I think originally the little reflector was meant to have a light behind it. that's the supply for it, through the courtesy light circuit Handy if you want to fit "puddle lights" .

[Penelope Stopit]

GJR said:

With the drop to 2V at the window power supply, and recovery to 12V over a few days, could this be an earthing problem? If so which earthing point would it be?

With the fault on the vehicle, you need to be sure that there is a good earth on one of the multimeter leads and then check for approx 12 volts switching to one motor cable when going for down and the other when going for up

Now the same test as above can be carried out but this time making sure there is a good positive on one of the multimeter leads

Testing as above will show if the negs and positives are switching or not and should give you a pointer as to what is failing

[Penelope Stopit]

David Beer said:

With this mod the windows go up twice as fast !

It's a cracking method of switching, any Momentary-ON push buttons will operate the relays

Bye Bye volt-drops

Several months ago RSI kicked in by the time the twentieth Lucar terminal had been crimped, the reward was certainly worth the suffering though

[GJR]

Penelope Stopit said:

David Beer said:

With this mod the windows go up twice as fast !

It's a cracking method of switching, any Momentary-ON push buttons will operate the relays

Bye Bye volt-drops

Several months ago RSI kicked in by the time the twentieth Lucar terminal had been crimped, the reward was certainly worth the suffering though

Is there any information on how to make and wire in this mod, or is it possible to buy it somewhere?

[Oldred_V8S]

Penelope Stopit said:

GJR said:

With the drop to 2V at the window power supply, and recovery to 12V over a few days, could this be an earthing problem? If so which earthing point would it be?

With the fault on the vehicle, you need to be sure that there is a good earth on one of the multimeter leads and then check for approx 12 volts switching to one motor cable when going for down and the other when going for up

Now the same test as above can be carried out but this time making sure there is a good positive on one of the multimeter leads

Testing as above will show if the negs and positives are switching or not and should give you a pointer as to what is failing

Just to add, you need the motor connected during this test. To run the test without a load will most likely show all is OK and leave you scratching your head. Always have a load connected when looking for voltage drops.

If this is dropping to 2v under load it represents a serious voltage drop. It shouldn't be hard to track down. Check all the connections for crud. The wiring TVR used was right on the limit. Heat along with a few years worth of corrosion will soon munch up all your current!

Some years ago I designed a relay mod which I have fitted to a couple of cars, (my own being one) and shared the diagram with a few others who have also reported a great improvement in the speed with which the windows open and close. I don't have access to the PC that has the file on and won't have for a week or so. If nobody else comes up with a design in the meantime I could draw it for you.

[Penelope Stopit]

GJR said:

Penelope Stopit said:

David Beer said:

With this mod the windows go up twice as fast !

It's a cracking method of switching, any Momentary-ON push buttons will operate the relays

Bye Bye volt-drops

Several months ago RSI kicked in by the time the twentieth Lucar terminal had been crimped, the reward was certainly worth the suffering though

Is there any information on how to make and wire in this mod, or is it possible to buy it somewhere?

Finding the below diagram saved me the time needed for drawing one



No explanation with it though, away I go

V+ Needs Fusing @ 20 Amps

"NO" Relay Terminals are terminals 87 on any standard 12 volt 5 pin relays

"COM" Relay Terminals are terminals 30 on any standard 12 volt 5 pin relays

"NC" Relay Terminals are terminals 87a on any standard 12 volt 5 pin relays

V - Is Earth/Return

"M" Is the window motor

The Relays Coils are shown but not numbered
Terminal 85 Is one end of a Coil
Terminal 86 is the other end of a coil

85 should be negative, 86 should be positive

To operate, 85 can be earthed and a positive switched to 86

To operate, 86 can be supplied with a positive and a negative switched to 85

In other words, the switching method is your choice (Switch Possies or Neggies)

One relay clicks for up and the other relay for down

As can be seen, there is a negative from the relays to each side of the motor

Switching one relay removes a negative from one side of the motor and applies a positive to it (up or down it goes)

Same as above when switching the other relay

Don't fit the relays in the doors as water can be a problem, they don't like it

Fit the relays as close to the doors as possible and run cables from them into the doors

[Penelope Stopit]

Here's the same circuit showing the relay coils connected for negative switching

This circuit reverses a door lock motor and is the same as the above

$$$Note$$$

The left hand relay coil terminals are wired incorrectly

Terminal 85 should be shown to the left

Terminal 86 should be shown to the right

The reason for the above is that some relays have an internal diode in parallel with the coil (Polarity Matters)



Below is the relay type used