Intermittent Brake Light

[fords4life]

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?

[Pebcak]

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?

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[Gary Lewis]

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

[fords4life]

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.

[Gary Lewis]

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.