Washer fluid level switch

[ChrisHC]

Has anyone any advice about renovating this? Mine works when out of the water but does show about 13 ohms resistance if I put a meter on it, and does not extinguish the warning light when installed.

After staring at it for some time I worked out that the lower arm houses a magnet that must activate a switch in the upper when it floats up to touch it. The magnet is rusty and perhaps is not the magnet it once was and does not pull the switch hard enough. I got a used one that was it better condition than mine but shows some rusting and also does not turn off the light.

Of course it is a bit unnecessary, you do know when you have run out of fluid because none appears on the windscreen, and the level is very visible when you look under the bonnet, but all the same I would like it to work.

[Brianmoooore]

Short the two pins of the plug together with a piece of wire and turn on the ignition to check that it is the switch at fault, and look carefully at the wires just where they enter the plug. These can break internally, leaving the plastic sheath still holding things in place. Pull on each wire gently - they shouldn't stretch.
The float slid over the shaft contains a magnet, and the shaft itself contains a standard reed switch. The hollow shaft is sealed, but eventually coolant seeps into it, and corrodes the very fine wires going to the reed switch.
It seems unlikely that the magnet has lost strength, but you can check by using a strong magnet held near the top of the shaft.
If you buy a new one, make sure you get the E30 version that screws into the top of a header tank. A similar switch is used on other BMW models, but these screw into the bottom of the tanks, and, if used in an E30 will turn the light on when the tank is full, but leave it off when the level is low.

[ChrisHC]

Thank you Brian, yes I have been shorting out the wires to extinguish the check light, but thought I would try to get it working. The wires had broken off where they enter the plug, so I dismantled the plug and cut away part of the plastic sheaths and soldered new wires on to the stubs, then reassembled the plug. It might be that fluid has leaked into the hollow shaft, as you say, and corroded the wires and perhaps the switch as well, causing the resistance I mentioned. Perhaps a drop in voltage caused by this resistance is sufficient to cause the check light to operate despite some current passing?

This is the washer tank I am talking about, not the header tank, and the switch is on the bottom of the tank not the top.

[Brianmoooore]

Ooops! Washer tank, not header tank! A lot of what I wrote above still applies though, although I don't think I've ever come across a failed washer level switch - most problems are simply that the switch has rotated in its mounting bush, and 'up' is no longer 'up'.
I've just put an ohmmeter across the terminals of the washer level switch in four different 6 pot E30s, (all working as far as I know, but no batteries in the cars) and all four show a resistance 12.7 ohms +/- 0.2 ohms when the tank is full, increasing to over 0.5M ohms with the tank empty, and all have a fairly rusted top surface to the magnets, so, whatever is causing your light to stay on, I don't think it's the switch.

[ChrisHC]

Thanks Brian. I have just been out to the garage to check the switch in situ, and it shows c13.2 ohms with the tank full. If I connect it to the loom, the check light glows, if I short out the loom the light goes out. If that is the normal level of resistance in the switch, as your investigation shows, then I am baffled.

I think I shall have to leave the loom shorted out and continue to rely on the MkI eyeball to assess the level in the tank.

[Brianmoooore]

Only things I can think of to check from here is that the brown wire from the switch is a good earth, and also the brown earth wire from the module in the roof (probably earths at the stud behind the glovebox).
It would be interesting to swap the blue/purple from the washer switch with the brown/red from the coolant switch, and see where and if the fault moves. Both are earth to keep the light off and open circuit to turn it on.

[ChrisHC]

The brown wire was a good earth and I then swapped the plugs over for the coolant level and the washer fluid level, which resulted in both check lights going out. So I pondered this and decided this must mean that the plug on the washer level switch must not be making good contact with the terminals on the switch. I put the plugs back as they should be and pushed down very firmly on the one for the washer level to ensure it was making contact. This was successful, when I turned the ignition on again the check light stayed dark. A very simple fault but so difficult the track down.

Thank you for coming to my aid once again Brian, without your expertise and the inspired suggestion to try the swap I doubt I would ever have got there

[Brianmoooore]

Lets hope it stays that way.
Wonder if moisture could have travelled down inside the plug from where the wires were damaged going into it, and corroded things?

[ChrisHC]

Possible, but I don't think so. The very ends of the wires had corroded and I cut those off, but the wire I exposed by cutting away part of the sheath was OK and I managed to solder to it so I do not think water had passed down it.