1995 Chevy Blazer brake light

That light comes on for 3 different reasons


1) Low brake fluid
2) Parking brake applied
3) Hydraulic problem in braking system

master cylinder is full of fluid parking brake is not on but the hydraulic problem where do i start i have replaced the lines from the master down to the combination valve but haven touched the abs pump i have a new abs pump but have not put it in yet dont know how to bleed it or if thats even the problem

If you have a good brake pedal I wouldn't even mess with the hydraulic system right now. Grab a large screwdriver, hold it by the blade and rap on the side of the master cylinder reservoir. Sometimes the float will stick when the reservoir is run real low.

brand new master i bled the master and bled the whole brake system any other ideas

As I stated, it's one of those 3 things. If you have a good normal brake pedal, you can pretty much eliminate the hydraulic issue. You could even have a defective sensor in the master cylinder. Try jumping out the plug.

how do i do that?

Unplug the sensor and jump the 2 wires together with a paper clip.

mine only has 1 wire a purple wire that plugs into the top of the combination valve

Your talking about the proportioning valve and I'm talking about the low fluid sensor in the master cylinder. The proportioning valve could be stuck too. You can find out by unplugging it.

One more thing we haven't covered here is the possibility that your truck has rear wheel only ABS. That system will put the brake light on when a code is present but will go out if the module is unplugged. $ wheel ABS doesn't work that way.
It also appears that you may not have a low fluid sensor in that model.