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Intermittent brake warning light

75MIKE

Sr. Member
Joined
Aug 22, 2001
Messages
955
Loc.
NE Washington
Some TLC on the 75 Bronco this spring. New ignition switch and bezel. New wiring harness from the firewall to the rear lights and sending units... and new brake warning light plug. New warning switch mounted in the brake proportioning block.

Started rig with new stuff, hey that's cool the warning light flashed when I brought the key back to run. Never seen that since I've owned it.

Went for a ride, 20 minutes later. I notice the warning light is back on. Pull over turn rig off and back on, light is off. 10 minutes, back on. I grew tired of this game.
What would cause intermittent light to come on and off with all new stuff?

If the piston was pushed over in the block would it stay on constantly?

I can see why owners pull the bulb now, but it would be nice to have things work as designed.

Thanks for the help.
 

SteveL

Huge chevy guy
Joined
Jun 24, 2001
Messages
11,608
Loc.
Hawthorne ca
It is a warning light. How's the fluid level on the mc? If low look for a leak somewhere. If thats all good then look for a loose connection in the wiring. Could also be an issue in the block on the frame. If it was working right before it's probably something simple.
 

Speedrdr

Contributor
Learning Member
Joined
Nov 27, 2017
Messages
1,134
Loc.
Paris, MS
Happened to me on a '72 with drum brakes all the way around. Mine had to do with low fluid level cold and would go off when fluid warmed up and expanded. Also light would come on when vehicle was driven on high angle side slopes.
Randy
 

half cab

Contributor
Guru Bronco
Joined
Dec 8, 2010
Messages
16,306
My booster have up the ghost last year and warning light came on.

New one installed n light went out.
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
This is a coincidence!
Yesterday I noticed the plug and wiring from the switch dangling under the frame. The plug is broken, but the light still comes on in its test mode.

If yours is coming on sporadically, the differential switch might have shuttled making contact but has a bad connection.

I can see the reason for this safety switch, but can't remember seeing a warning light like this on other cars.

I'm considering just eliminating the switch, and use the light instead to add a parking brake indicator. Driving with the parking brake on has become a problem in my household. I'm not blameless either.%)
 
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