Brake Pad Warning Circuit

[Klevy]

I have an 89 325i manufactured in 11/88 and my brake pad wear/warning light is always on. The rear harness was cut off by a PO or a mechanic... So I went to a junkyard and picked up a new harness end so that I could plug in the pad sensor and get that blasted light to got out. After I raised the car and got out the soldering kit out I looked up and there are three wires dangling out of whats left of my car's harness, yellow w/green stripe, blue and brown. The section of harness that I got out of the junkyard has two wires, black and brown.

So I did some Googeling and in similar threads the response is that the three wires are part of the ABS system... According to the wiring diagrams available at: http://www.armchair.mb.ca/~dave/BMW/e30/ the ABS system uses two wires to each wheel sensor I can verify this in the front by disconnecting each sensor at the yellow connector in the engine bay. And to make matters worse the same wiring diagrams say the brake wear circuit is two wires...

After that helpfulness I got out the old trusty multimeter and started testing voltages and continuity at the three wires and got no where. None of the wires is a ground, any voltage that I get is inconsistent (sometimes I get 1-2 volts and sometimes I get 0 when testing the same wires). These results are the same at the front sensor as well only its harness is intact and the sensor is good. Oh and when I tested the front none of the three wires in the back where touching. So I'm thinking i have a short (I hate those) somewhere...?

Sorry to ramble on a bit but I have been trying to figure this one out and the e30 is determined to give me a headache :( But I have not completely given up hope (pulling the bulb), if any one has ideas they would be much appreciated!!!

[stamar]

I want to encourage you to do it right if you want to

http://www.turnermotorsport.com/BMW-E30/c-133-bmw-brake-pad-wear-sensors-abs-sensors.aspx

heres the parts.

I hope that helps. I know when I looked into it personally, I decided that electrical wear sensors are actually potentially dangerous to rely on and that you should rely on using pads with audible wear sensors.

I do believe the e30 brake pad sensor system doesnt meet safety standards.

[kinvodA]

Also, if it flickers randomly, it could be the board, hopefully I will get to try this today:

http://www.e30tech.com/forum/showpost.php?p=570487&postcount=13

[Gregs///M]

The cluster sends 12V power to the passenger rear sensor, through the wear sensor, then up to the front drivers side, through that sensor and back to the cluster. Any short or open circuit will cause the light to stay on.

Download the electrical troubleshooting manual located in this site. It will have complete diagrams of the brake wear circuit, including color codes. It will also help you restore your ABS or speed sensors at the wheels.

[stamar]

http://issuu.com/stamar/docs/1989_bmw_325i_-_325is_electrical_troubleshooting_m

I have the 89 one posted online. I forgot for a second you had the same year as mine.

[kinvodA]

I fixed mine yesterday with a little bit of soldering action, the light hasn't come on yet. Unfortunately, now my cruise control isn't working, there should be no connection...

[g.ruff561]

My brake pad warning light is out permanately. I soldered and heat shrink wrapped the 2 wires together, then zip tied the wires up out of the way. This closes the open circuit. No more brake pad warning light. However you must do a visual check of your brake pad wear. I do mine about every 3 months. Not for everybody but it works for me.

[dogsbark26]

Cruise Control Connection

I fixed mine yesterday with a little bit of soldering action, the light hasn't come on yet. Unfortunately, now my cruise control isn't working, there should be no connection...

Did you remember to reconnect the cruise control to the green connector on the back of the instrument cluster?

[Klevy]

Thanks for all the advice! I had a cracked solder joint under the temp gauge. Fixed that and the light goes out when bridging the blue and yellow/green wires, still no idea what the brown wire is for. I connected the new harness end and sensor and the light goes out but flickers on every once in a while, I think my splice is loose.