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Intermittent Brake Light

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fords4life

Intermittent Brake Light

So....the next problem to solve is an intermittent brake light. It comes and goes, and I do have a softer pedal when it is on, but if the pedal does come back and brakes feel ok again. Truck does stop and pedal never goes all the way to the floor. Entire booster/master cylinder assembly was replaced not too long ago. Thoughts on where to start? Could it be a bad proportioning valve?

1986 F-150 SC 2wd 4spd 302EFI Base Model all OEM motor/trans/emissions equipment.

Pebcak

Re: Intermittent Brake Light

Possibly the switch going out at the Brake Booster and pedal?

On Mon, Aug 6, 2018, 18:22 fords4life [via Bullnose Enthusiasts] <[hidden email]> wrote:

So....the next problem to solve is an intermittent brake light. It comes and goes, and I do have a softer pedal when it is on, but if the pedal does come back and brakes feel ok again. Truck does stop and pedal never goes all the way to the floor. Entire booster/master cylinder assembly was replaced not too long ago. Thoughts on where to start? Could it be a bad proportioning valve?
1986 F-150 SC 2wd 4spd 302EFI Base Model all OEM motor/trans/emissions equipment.

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NAML

1986 F150 XLT Lariat, 4X2, 351W, 1406 Edelbrock Carb - Currently going through an engine rebuild through a "Father/Son Project"

Gary Lewis

Re: Intermittent Brake Light

Administrator

In reply to this post by fords4life

Just want to make sure I understand - is it the rear brake light that is intermittent, or the brake warning light?

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

fords4life

Re: Intermittent Brake Light

Gary Lewis wrote

Just want to make sure I understand - is it the rear brake light that is intermittent, or the brake warning light?

Sorry. The warning light is intermittent.

1986 F-150 SC 2wd 4spd 302EFI Base Model all OEM motor/trans/emissions equipment.

Gary Lewis

Re: Intermittent Brake Light

Administrator

In that case it may be the "proportioning valve", which is really the pressure differential valve. It is really just a piston that is moved one way or the other if there is a pressure differential between the front or rear system. And if it goes to one end or the other it grounds the lead to the warning light.

Usually the valve itself doesn't go bad, although I have had them stick. But what usually happens is that the pressure does fall in one end or the other. It could be that you have air in the system. Or low fluid levels caused by a leak. Or, a bad master. But an intermittent warning light is probably not the valve.

Gary, AKA "Gary fellow": Profile