Master window switch "fix" idea

[Huskymaniac]

I looked at the wiring diagram and there are two wires going to each window motor. The master switch either sends two grounds for off or a ground and 12V for on and which wire gets which depends on the desired motor direction (up or down).

The problem with the switch is that the contacts wear both electrically and mechanically. And the current has to travel through two contacts and two long wires so there is a lot of voltage drop. Since 12V and GND are not available at each window, we can't do much about the wire resistance. But we can do something about the contact resistance.

I am thinking of putting a single pole, double throw relay on each wire. So, 8 total relays. Each wire will get either 12V or GND depending on what voltage is driving the relay coil (or photodiode for a solid state relay). For a regular relay, the normally closed contact will be tied to ground and the active contact will be tied to 12V. The relay coil will be tied to GND on one end and the line coming from the master switch on the other. When it goes to 12V, the relay output will switch to 12V. There are 10 wires going to the master switch. 8 for the four window motors, 12V and GND. The wires can be cut and two connectors placed on the box with the new relays. One will go to the master switch and one will go to the window motors and the incoming 12V and GND lines. The 12V and GND will be used to provide the 12V and GND power for the relay outputs as well as the GNDs for the relay coils. 12V and GND will be passed to the master switch and the master switch will send out 12V or GND on the 8 lines between the relay box and the master switch.

The relay I am thinking of using is 551-EX2-2U1S from Mouser. Each has two SPDT relays so four would be needed. I can make the simple PCB on my board maker at work. This relay operates on only 75mA and switches at 6.5V so even the weakened contacts in our master switches should be fine to drive that. The relay contacts are made from a silver alloy and have a closed resistance of only 4 mOhm! Basically, the windows should respond like they did on day 1.

Am I missing anything?

[irox]

Ages ago I wrote a mini how-to for rebuilding the switches, but it was posted on the other SVX forum which vanished...

From what I remember, the issue wasn't just with the contact resistance, but there are metal clips in the switch which flip back and forth (kind of like "oil canning") and loose their shape after while and no longer touch the contacts. This may mean some switches are just always open, rather than dealing with high resistances at the contact points (although easy to check).

The how-to did contained instructions for bending the contacts back to the right shape. It wasn't hard, but I remember it being a little counter intuitive (like string a bow when you know nothing about bows). Maybe somebody has a copy of the how-to some where? (Or I can write it again when I have deal with a faulty window switch).

I do like the idea of switching to relays or solid-state controls, this give us a lot more flexibility on other modifications (adding remote window windup feature for example).

Good luck!
Ian.

[Huskymaniac]

Originally Posted by irox

Ages ago I wrote a mini how-to for rebuilding the switches, but it was posted on the other SVX forum which vanished...

From what I remember, the issue wasn't just with the contact resistance, but there are metal clips in the switch which flip back and forth (kind of like "oil canning") and loose their shape after while and no longer touch the contacts. This may mean some switches are just always open, rather than dealing with high resistances at the contact points (although easy to check).

The how-to did contained instructions for bending the contacts back to the right shape. It wasn't hard, but I remember it being a little counter intuitive (like string a bow when you know nothing about bows). Maybe somebody has a copy of the how-to some where? (Or I can write it again when I have deal with a faulty window switch).

I do like the idea of switching to relays or solid-state controls, this give us a lot more flexibility on other modifications (adding remote window windup feature for example).

Good luck!
Ian.

I opened up an old switch and you are right, it is a combination of mechanical and electrical. The metal strips flatten out over time which reduced the force applied to the contacts. And the contacts oxidize over time which increases the resistance.

What I don't know, because I didn't de-solder the thing, is if there is some intelligence in the electronics in there. For example, what enables the auto down and auto up feature? Is there a sensor for when the window stops that senses the increased current draw or is it simply a timer and the limit switch in the motor stops it when it reaches its desitination? My approach would defeat any kind of current sensing.

[irox]

Ah yeah, I think it might have been a timer, I don't remember exactly where that was. I vaguely remember something about it being piggy backed on some other module, but it's been a while since I had to trace those lines....

I don't remember any fancy electronics being in the switch assembly. I was able sand the contacts and reshape the metal clips to get it working again. I was skeptical that it wouldn't work for long, but it ended up lasting years (and as far as I know it's still going strong).

[irox]

I took a quick look over the FSM manual wiring diagrams and I don't easily see how the the auto up/stop part worked, I would have to spend more time tracing to figure it out...

For the timer comment, I was probably thinking of the door-lock timer or something.

Sorry I don't have anything more useful there.