On your car (and mine) the brake failure light is lit when a switch closes in the brake line distribution/junction block. The switch closes when the pressure in one of the brake circuits differs from that in the other circuit.

That can happen if there is a fluid leak in one circuit. BTDT. Look at the ground just inside and to the rear of the left front wheel. If there is evidence of a leak, it is the junction block.

Look at that block. You can find it easily. Find the two fluid lines coming out from the master cylinder. They both go straight down to the block. Look down the lines and you'll see the block. It has eight line connections and a wiring harness on it. Looks like a metal spider, sort of.

If it's wet, it leaks. Check the brake fluid reservoir every morning and evening. See if the level is down in one tank part and not the other. Get a small can (not the 32 ounce) of DOT 4 brake fluid, and top up the reservoir. Use care, fluid damages paint.

Good Luck,

Bob

:>)

PS: If you can change oil and filters, and have a few tools and the nerve, you can change a master cylinder. It can be done without bleeding. The junction block is a bigger job, and absolutely requires a brake system bleed.