Brake light illuminated after release

Thunderbird83

Registered User
1991 Thunderbird SC, ABS.

Bought the car 3 months ago. At the time of purchase, it was having the classic bad accumulator symptoms (brake and abs lights would illuminate when pressing the pedal, and the motor ran with every press.) I replaced the accumulator ball, and all was well, until...

A couple of days ago, a new symptom appeared. When I release the brake pedal, the brake light will illuminate for about 5 - 10 seconds. Braking action is fine, and even with the brake light illuminated, there is good pressure. I checked the fluid level, and it is full to the "accumulator charged" indicator on the reservoir. Still, the light illuminates almost every time I release the brake pedal (like when I'm accelerating from a stoplight, etc.)

Any ideas? What could be the matter?
 
I'm still trying to figure out what is causing this. I added some additional brake fluid, and the light did not come on for one drive. Then it came back same as before. The fluid is now above the "full with accumulator charged" line.

Help. Anybody got any ideas?
 
It might be a bad level switch at the MC, or it could be a bad switch or loose wire inside the console, where the handbrake is. Maybe it tilts and makes contact when you accelerate.
 
My problem is now evolving... The brake light (idiot light) is now illuminated almost all the time. Today, the Antilock light has been coming on for brief intervals at times when the brake pedal is not applied (usually shortly after releasing the pedal). The accumulator seems ok, as the pump motor only runs after every 4th pedal press.

Braking action is still normal, and pedal pressure is just fine. I did notice, that the rear brake lights don't come on with light pressure. It takes at least moderate brake pedal pressure for the rear brake lights to come on.
 
OK... now both the brake and antilock lights are illuminated all of the time. I can't find any info about what that means. I found info about brake and antilock illuminated with hard pedal, but my pedal is normal.
 
My thought is it's an electrical problem....

Most likely a bad wire somewhere could be causing the lights to come on....
 
On the front of the control valve (would be a master cylinder on non-Teves Mk II designs), is a ground wire.

This ground wire needs to be removed, the aluminum control valve polished slightly (400G or so sandpaper to remove oxidation), the terminal polished (the one the screw goes through), and then reassembled.

See how that helps your lights.

On mine, when that happens, it means I've lost another caliper (three so far in two months!) and the fluid is low ...

RwP
 
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