Just recently had my brakes serviced (new front/rear pads, front rotors re-surfaced) and now today the dash brake warning light on my '91 300E began to blink, slightly and rapidly. I suppose more like a flutter than a blink, it is so rapid. Color is never solid, and blinking goes away when I apply the brakes, but returns when speed is achieved. I removed the sensor connected to the brake fluid resevoir but problem persists. Other than this, the brakes work perfectly normal after the service. Any ideas what's going on here? What exactly does the dash light sense? Thanks for any ideas you have, -Paul-

How about the front brake sensors...the ones that inform you of pad wear? Perhaps they weren't installed properly?

Just a guess...

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The amber-colored light with the ((O)) emblem is for the pad sensors only. The red colored BRAKE light is usually, and I "think" only for either low brake fluid, which you've done the exact test I would have done, OR for the parking brake switch, which means the parking brake is applied. There may be some problem with the switch for the parking brake. The switch is located at the parking brake pedal mechanism itself.
Gilly

You have a problem with one of the four brake pad sensors or the wiring going to them.

ps on that:
If it does this quite often, as a test, try pulling "up" on the parking brake pedal when it starts to flicker, see if a slight upward pressure will make the flickering stop. I would try doing this with the top of your foot, not by hand, and only if it's safe to try it. Don't want ya to hit the south side of a north-bound Freightliner or anything!
Gilly

Paul:
I see everyone else feels it's a sensor problem. We need to know if it's the amber or the red light that is coming on. If it's the amber pad warning light, I whole-heartedly agree that someone probably just messed up on one of the sensor wires, this happens occasionally. If it's the red one, then I stick to my idea of the parking brake pedal switch. If ends up not being the parking brake pedal switch, then it may be that someone had the cluster out and misinstalled the bulb. These mostly have seperate wiring and can be installled into the wrong "window" in the cluster causing all sorts of confusion, for example the low washer fluid put into your "BRAKE" window will make you think there is a brake problem when actually you are just low on washer solvent!
Gilly

Thanks guys for the help:

Yeah, its the ((O)) amber light, not the red one. I guess the tech didn't fully push in one of the sensors. I'll yank the wheels off and find the loose sensor.

Thanks alot y'all!

~Paul

Paul:
A loose connector won't cause it. The circuit looks for a ground, so you're looking for one of the wires to be cut into, just nicked a little, causing a path to ground. You can yank all the sensor wires out and that light will never come on (normally).
Look in the area of the anti-rattle clips between the pads, or the wire can actually just be rubbing against a rim, which is tough to catch if you don't know "it can do that", because you pull off the offending wheel, and "what a ya know", it's not rubbing ANYWHERE now!
Gilly

would a cut on the sensor wire, causing it to ground when touching metal when car is moving, cause the amber brake pad sensor light on a 87 560SL to flicker intermittently?

does not come on when I use the brakes, just when the car is moving, usually at above 40mph or so...am thinking perhaps at speed the wind pushes some wire against metal and if the wire is cut somehow.....

they just replaced the two front wheels on the 560SL before I picked it up yesterday and drove it home from Texas...I wonder.

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Dom:
Yes, they will come on at the darndest times. Could be as you say, a mis-routing of the wire to the sensor. If the car has ASR, it has rear sensors as well, so don't forget to check those. It could be related to the wheel changing, but of course when inspecting for clear routing of the sensor wires (in the caliper area) be sure to make sure the pads aren't actually worn out, which is what the pad sensors are supposed to be warning you about!
Gilly

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The problem was indeed a sensor wire that had not been pushed in all the way. So Gilly, I suppose my problem was an exception rather than the rule.

Thx for the help,

Paul

Paul:
The system operates by the sensor wire contacting a ground. If the sensor itself isn't plugged in, the light won't come on, unless there is a ground source in the body harness instead of the sensor. So the sensor wire must have been touching a ground source somewhere, then you moved it so it wasn't touching anymore, maybe you didn't realize it, or else I misunderstand what you mean by "sensor wire that had not been pushed all the way in".
Gilly

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thats ok paul i know what you meant

I think Paul was talking about that semi-circular shaped thing that plugs into the brake pad. That thing makes a ground contact when the pad wears and if it is fully pushed into the pad.

If it is not fully pushed into the pad, then it makes an early contact so the light.