by Barnes » 29 Feb 2012, 08:32
There are two circuts assosiated with the brake warning lamp (named that to denote it illuminates when there is an issue in the brake system). One is the parking brake handle, which uses a normally open button-type switch which closes when the lever is pulled. The other is called the "pressure differental switch" which is located underneath the master cylinder inside the combination valve (brass block with brake lines going in from the master cylinder and going out to the wheels). You will see a single wire connected to the combination valve. If you unplug this wire and the warning lamp goes off, the pressure differential switch is activated, meaning there is an unequal amount of pressure going to the front and rear brakes. A leak or air pockets in ONE SIDE of the system will cause the switch to activate. You must inspect all brake lines and fittings for leaks and repair as required. If no leaks are found, completely bleed the front and rear of the system. If the light is still on after bleeding, remove the switch from the combo valve and manually recenter the plunger. No TM will have this info, but if you search "combination valve / pressure differential switch" you can find a diagram of what it looks like and what parts have to be moved where.