How sensitive are the brake wear sensor wires??!? - PeachParts Mercedes-Benz Forum

JHZR2 · #1 03-16-2011, 09:12 PM

So I did the steering and all on my 82. I also replaced brake lines as they were bad. To do this simpler, I pulled the wires gently out of the little clips to get them out of the way...

Well I started the car for the first time since doing this stuff tonight. Slight, dim glowing is now coming from the brake wear light... UGH!

I have plenty of brake pad. I cant believe the wires are this sensitive, but maybe they are... Just due to age. Anyone else ever encounter this?

Im hoping some good jiggling of the wire fixes this... How annoying.

Thanks!

aaa · #2 03-16-2011, 09:22 PM

They are on/off. The rotor wears thru the pad til the wires are exposed, then wears thru the wires' insulation, at which point they ground to the rotor and light the light up.

So accidentally grounding them anywhere else will light it up too. I'd unplug them and see if it still lights up, that'll tell you if it's the wires or the actual harness (that could be grounding too...) to them that's bad.

JHZR2 · #3 03-16-2011, 09:26 PM

Can you remind me where the user replaceable section plugs in versus the harness? As I recall there is a harness connection point under the battery and I guess on the other side... But the actual lead from the pads is much shorter...

Thanks!

Palangi · #4 03-16-2011, 09:26 PM

Sometimes the gromet wears out where the harness passes through the fender well, causing a short that turns on the light.

tangofox007 · #5 03-16-2011, 09:47 PM

Quote:

Originally Posted by JHZR2

Can you remind me where the user replaceable section plugs in versus the harness?

At the calipers.

http://catalog.peachparts.com/ShopByVehicle.epc?q=1982-Mercedes--Benz-300d-Brake&yearid=1982%40%401982&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6190%3AED%7C10000135%3AMBC%7C1504%40%40300D&catid=241658%40%40Brake&subcatid=241669@@Brake+Pad+Sensor+%2D+Front+and+Rear&mode=PD

JHZR2 · #6 03-16-2011, 11:02 PM

right, but there is another connection point inside the fender wall...

Stretch · #7 03-17-2011, 04:18 AM

Did you put in new sensor wires at the brake pads or re-use the old ones?

JHZR2 · #8 03-17-2011, 07:44 AM

I had no reason to. Plenty of brake pad left. All I did was unclip the wires where they are attached at the interface between the hard brake lines and the rubber ones. Im thinking that just bending them a bit must have damaged the innards of the wire, as I have never had the light before...

vstech · #9 03-17-2011, 08:14 AM

have you verified that the little wires from the pad to the caliper socket is not cracked and grounding? did you take the calipers off when you changed the hose? if so, you may have pulled the insulation off where the wire follows the shock...
the harness pulls off in a large connector near the glow plug relay I think... just unhook the wire from the caliper, and unclip it from wherever it goes up the wheel well, and jiggle the wire until you find it inside.

toomany MBZ · #10 03-17-2011, 08:15 AM

The attachments show that part, there is a left and a right one.

Stretch · #11 03-17-2011, 09:17 AM

Quote:

Originally Posted by JHZR2

I had no reason to. Plenty of brake pad left. All I did was unclip the wires where they are attached at the interface between the hard brake lines and the rubber ones. Im thinking that just bending them a bit must have damaged the innards of the wire, as I have never had the light before...

A good clean up will also help - just in case you didn't do one. One can of brake cleaner and who knows...

JHZR2 · #12 03-17-2011, 11:39 AM

The light went out... Guess the line corrected itself... Weird. I think it is a little short in the line.

toomany MBZ · #13 03-17-2011, 11:55 AM

First pic is of the right side, you see some of the insulation is failing, works AFAIK.

Second is the left side, the black rubber line.

When I purchased the SD, I asked the seller what that line was hanging down near the drivers front wheel. He didn't know. It turned out to be the left harness, broken off at the caliper, so there was no connection, the dash light was not on.

patbob · #14 03-17-2011, 08:11 PM

Quote:

Originally Posted by JHZR2

To do this simpler, I pulled the wires gently out of the little clips to get them out of the way...

Well I started the car for the first time since doing this stuff tonight. Slight, dim glowing is now coming from the brake wear light... UGH!

I have plenty of brake pad. I cant believe the wires are this sensitive, but maybe they are... Just due to age. Anyone else ever encounter this?

Yup, they're that sensative. I pulled them out of the pads to check the brakes when I first got my car, and afterwords they would ground through the pad material and turn the light on. Worse when it was wet out, usually go away if it was dry. Apparently they have a little end cap to seal them that sticks down in the pad and pulls off when you pull the wires out. Then they can conduct.

It was early on when I was having the indy do some of the repairs and didn't know what I'd done wrong. Had him take a look and they replaced the wires for me. We get wet for 9 months straight every year, so there was no way I was going to ignore that annoyance.