Mine started coming on late last week, intermittently, but often. I had planned on flushing the brake system by spring or summer, but was kind of forced to do it this past weekend. I knew that the brake pedal seemed just a little softer than I had felt it in the past, but not bad. It certainly didn't get spongy as I held it down (a usual sign of MC seals going). Anyway, after bleeding the system and the MC, the pedal firmed up quite nicely (fluid level had never been low), and after test driving the light stayed out. While some techs I spoke with thought the sensor might have just been getting flaky, since it's staying out now it seems like perhaps it was indicating a genuine fault. I haven't seen any way to replace just the sensor; 4Crawler pointed me to the heavier duty 1" bore MC when I do decide to change it, but I was wondering about the light coming on in the first place. When the MC definitely went out on my (now sold) Honda, the pedal got soft but the light never came on. Can moisture content in the fluid be enough to make the light come on?

BTW I now see synthetic hydraulic fluid on the market. Is it OK to mix it with conventional?

I've got an87 pu. The cap on the MC has a float sensor which turns the dash light on when fluid is low. Also I don't know for sure but what about the parking brake. Is there possibly a switch that turns the light on when handle is pulled. I know other vehicles have this.

No, I checked the e-brake, and it isn't the problem. It will switch the light on and off just fine (and when the light had stayed on I kept the e-brake off and pulled the sensor plug, which killed the light).

My official '94 service manual makes it look like the sensor is in the cap, but it clearly is not. The book shows wires coming off the cap, but mine has the plug on the side of the reservoir. I *think* it's the original. When I got the rig it had 57K miles, I question that the PO had changed the MC by then. I've got 194K on the truck now, I just wish more of those miles were on dirt!

I think the point canuck is trying to make is that the E-brake and your fluid sensor both share the same warning light indicator. I have the same problem and after replacing pretty much the entire brake system the light still flickers every once in awhile. I wasn't chasing the intermittent light problem by replacing everything. The parts needed to go anyway. The point is, my warning light flashed occasionally before and after everything was replaced. I chalked it up to a loose wire in the instrument panel.

Check the float sensor on the MC reservior and the E-brake indicator. If those are fine then it's most likely in the wiring harness or instrument based problem.

PS. The Valvoline Synthetic brake fluid is awesome and is compatible with DOT 3 and DOT 4 fluids. That's what I run in everything.