Brake pad wear sensors

[GTXcess]

The warning light keeps coming on and going off on the dash when I'm driving so I had a poke around at the front offside over lunch to see if I could see the problem. My eyes were immediatly drawn to what looks like the pad end of the sensor cable which has black electrical tape over the end and is attached to nothing.

As this is my 1st E30 I don't know what it is supposed to look like ie is the sensor part of the brake pad or is this a separate part and where would I find it? There is another cable to the hub which i assume is part of the ABS warning and that looks fine.

So the exam question - where is the sensor at the front, and if I have no sensor, whay is the light going on and off intermittantly?

Confused

[Brianmoooore]

Sensor at the front has been 'rigged'. They are not resettable, and once tripped, need replacing, along with the (presumably) worn pads. Around £4.50 from BMW, or about £2.50 pattern, IIRC. If you have rear discs, there's another (different) sensor on the rear right.
For the flashing warning light, use the forum search function to look for "220 ohm" and my username, which should lead you to the solution.

[daimlerman]

Pad sensor works by having a loop of wire enbedded in a plasic block.When the block is worn away,the exposed wire shorts to earth and the light comes on.Disc braked cars have a sensor at the rear as well.The sensor should have a connector block close by,to enable it to be re-newed each time the pads are replaced.If the wiring is intact and the pads unworn,the problem may well lie in the instrument circuit board,there is a resistor close to the temp. gauge that fails/develops a poor joint.In this instance,do a search using Mr Moore's user name and 200(I think!)ohm resistor.

[Brianmoooore]

Type faster, Mr. daimlerman!!

[GTXcess]

So the sensor is not integral to the pads. If not where does it sit when fitted to be able to wear at the same rate as the pads? Also if the wiring has been rigged, what prevents the light coming on most of the time?

[Brianmoooore]

Pad sensor is a 'D' shape, and fits in a recess in the friction material of one of the pads. Occasionally you may come across aftermarket pads which have no provision for the sensor though.
As daimlerman said ( if a little late), the sensor is simply a block of plastic with a loop of wire embedded in it. The warning light comes on if either the wire is bared and comes into contact with earthed metal (usually the disc) OR is worn right through and becomes open circuit.
The two ends of the leads that went to your sensor will have been bared, twisted together and insulated.
If you fit a new sensor, take care to dress the wire properly where it comes out of the calliper, or it will wear through on the inside surface of the well of the wheel.

[GTXcess]

I'm with you. Discs look ok but pads are about 2/3 worn and have no recess so a set of pads are going on the shopping list and a wear sensor. Many thanks for the clear advice as ever.

[Brianmoooore]

Check the thickness of the discs before you invest in new pads - E30s eat discs at the rate of about a set to every two sets of pads.
Minimum thickness is 20.4mm.

[GTXcess]

Just been and bought some pads and a sensor and I note that the sensor has a connector block which presumeably is supposed to mate to the one on the car. Problem is my car has no connector block as a previous owner has cut it off (I presume) and crimped the wires together with a connector. Is there any drama with cutting the block off the new sensor and just linking the wires together, or should I be trying to replace the cable on the car to get a new plug?