Merc 190 leccy windows.

[arceye]

Hi Chaps,

The Mercedes is back home and on the road,

However on buying her back the electric windows have been intermittent. Sometimes working, sometimes not. They have now packed in altogether.

A little knolwedge being dangerous, and me and lectrickery not being great friends beyond the most basic wiring...................

I have determined that the windows ( only has leccy front ones) are supplied by two seperate fuses and a relay in the fuse box.

I first checked fuses and then had the switches out and supplied power directly to two of the terminals of the plugs and windows worked.

There was no clicking from the relay in the fuse box so I pulled its cover off and tried cleaning the contacts but no joy. If I manually close the points of the relay by slipping a bit of card between the off position post and contact then the windows work.

So I'm guessing next to try is a new Relay?

Though I have a few relays knocking around mine are all "ordinary" spade connection ones whilst this is a slightly odd (to me) round pin one, and it will be a few days or so before I can get one up.

In the meantime how likely am I to burn the vehicle to the ground if I temporarily force the contact points closed with afore mentioned slip of card? I do know the relay is there for a reason, I'm not normally into bodgery so would undo it as soon as I can try another relay but working windows are pretty handy.

Don't be too hard on me for my Heath Robinson ways

[harvey]

If you bypass the switches and the windows work then it won't be the relay, as that's operated by the feed from the switch. Sounds more like faulty switches to me, but my knowledge of Mercs is limited to say the least (putting an engine back together that arrived in bits in the boot), and electrickery not a lot more.

[harvey]

Sounds more like faulty switches to me,

PS

Or a loss of supply to the switch if you're putting a direct live to the switch rather than bypassing it.

[arceye]

Cheers Harvey,

Yes, was putting a seperate supply to the switch to check the problem didn't lie between there and the motor.

What I have now done is borrow an identical relay off someone just to check, but it made no difference.

However with my limited knolwedge I think there should be two live feeds to the relay (haven't got a diagram for this car), one to post 30 always live, and an ignition switched live to post 86. This means when you switch on the ignition the power windows become live as the relay completes the circuit.

If anyone has any real knolwedge on this sort of thing please feel free to put me right, this is just from trying to figure out how the system works, and a little vague internet searching (told you I was dangerous)

If I jumper these two posts together the relay now clicks on and the windows work as they should, but then with the ignition off the relay remains live and windows still work, which can't be good.

So, IF I'm right about the live feeds, then it looks like I have lost the ignition feed to the relay. I think I need to have the fuse box out and check the wiring going to the relay, and see if I'm right, then perhaps replace the ignition switched feed.

Does this sound at all plausible?

I think I'd better try and get a manual with a good wiring diagram!!!!

[pryantcc]

Arceye, I'm not convinced.

I would have thought that the switch was what "sent" the second feed to the relay. The idea of the relay is that it takes the load off the switch. So the switch is only switching a small load (the relay) and the relay is switching the big load (the window motor). Are there electric windows on the back? can you try swapping the switch for a known good one?

[tractorman]

I thought the relay was used so that the ignition could "control" the windows - ie they would only work if the ignition was on (to stop kids trying to strangle themselves while playing in the car). In that case, as arceye suggests, I'd have thought that the relay is there to reduce the current through the ignition switch.

Not that I know much about "posh" cars!!

[suffolkpete]

Are the windows "one touch" operation. If so, then the ignition feed probably operates the relay and the other feed sustains operation after you've released the switch. Really though, yuou shouldn't undertake any sort of electrical work without a wiring diagram, especially on anything that complicated.

[arceye]

Cheers chaps,

Windows work only when switch is actually pressed, no one touch or anything fancy.

After quite a bit of looking and fiddling I'm pretty sure the system goes something like this,

One main feed from Battery to Relay, one feed from Ignition to Relay to switch the Relay.
Relay then goes to two fuses (one for Nearside Electric Window, One for the Drivers Window), and that the power from the fuses then simply powers the window circuits via the switches.

I'm 99% certain now that the relay is only there to serve the purpose of making sure the windows only operate when the ignition is on, and so is simply removing the load from the ignition switch as Tractorman suggests.

So I think I have lost the ignition feed. If I jury rig a feed to the relevant terminal of the relay then everything works as it should but A diagram indeed would deffo be handy to confirm this as Pete says, I think a little work with the multimeter might do in the meantime, though I will get hot on the heels of ordering up a workshop manual.

Wish me luck.........