The was a sensor coming off the proportion valve at one point, someone took it off and put a plug where it goes and the harness for it is just hanging. My brake lights do not work and I think this is the reason, anyone know where I can buy one of these? It's on a 1968 f100 lwb 3 speed with 5.0.

 

https://www.npdlink.com/store/produc...301-50000.html

 

Your brake lights switch is under the dash on a bracket. It is abut 3" long and is threaded to allow adjustment.
The plug in the valve is probably factory. so leave it alone.

 

Thanks ultra ranger, great help. No milliam, the harness for the sensor is hanging right by the proportion valve. Looked up a diagram and it goes to that sensor.

 

But yes I do have a switch under the brake pedal as well.

 

Be that as it may. That connector has absolutely *nothing* to do with the brake lights. The only light that it would actuate is the brake failure light on the left side of the dash just below the instrument panel.

 

You will have a switch connected to your brake pedal, check that and trace all the way back to your tail lights, could very well have a bad bulb or broken wiring

 

It's a brake circuit failure switch... not a brake light switch.

If the front or rear hydraulic system fails, then the low pressure created by that side results in the internal piston sliding to towards that circuit of the prop valve (or distribution valve) and actuates the warning light.

The switch is normally open. Its pin sits in a V-groove.. awaiting.

 

The first time I read and replied to this I was at work and didn't take time to completely read what was said (I was in a hurry). I saw the part about the brake valve and its switch but didn't catch the part about the brake lights not working.

If the plug on the brake valve switch is disconnected and the brake lights do not work, then this is two different problems.

If the brake lights don't work, the problem is either the brake light switch on the pedal, a wiring/fuse/socket problem or both bulbs are burned out.

The plug being disconnected from the switch on the brake pressure differential valve indicates one of two things: there was a failure of a brake component at one time that caused a drop in the hydraulic pressure in the brake system that tripped the warning light on the dash or, someone serviced the brakes, went to bleed them out causing the pressure differential valve spool to shift and it turned the brake warning light on.

Evidently, they didn't know how to recenter the pressure differential valve spool so, in order to turn off the annoying brake warning light on the dash, the connector was simply unplugged and the switch removed from the valve body. The dash light went off as a result of this but it didn't make the problem go away. --The pressure differential valve spool is probably still shifted off-center. You'll know if you install the valve switch, plug the connector back in and the warning light on the dash comes back on and stays on.

 

This switch has nothing to do with the brake (stop) lamps.

C8AZ-2B264-A .. Brake Pressure Differential Valve Warning Lamp Switch / Available from Ford & auto parts stores.

Applications: 1968/70 Passenger Cars / 1968/79 F100/350, Bronco & Econoline.

When this switch goes bad, the Brake Warning Lamp (shown in pic as 10A840 at far left corner of the dash) comes on...and stays on.

A previous owner was unaware, so took the switch off and plugged the hole. Could have just pulled the wire harness off and left the switch in place.

 

I suspect there's a very good chance there was never anything wrong with the differential valve switch. The problem was most likely the pressure differential valve spool shifted, closed the switch contacts and the warning light came on and stayed on because they probably didn't know how to recenter the spool to make the warning light go off. Removing the connector (and in their mind, the switch too) was the simplest remedy to the situation of turning the warning light off.

 

OP has at least 2 problems for sure. As for the brake lights, as stated above check the brake switch,circuit, bulbs, and the tail lamp wiring along the frame back by the L/R tire. Those connectors there are usually hacked by people hooking up trailer lamps
Now for the plug in the Brake Pressure Differential valve. I think the seals on one or both sides of the v shaped internal piston inside the Brake Pressure Differential Valve are bad and leaking. Back in those days I can't tell you how many customers thought the brake failure warning switch was supposed to hold the brake fluid and it's pressure that was leaking from it's center. Right at where the wiring connector snaps on to the switch. It's not and it can't. There is no way a plastic/nylon bodied switch could hold back that much pressure. And plus there isn't supposed to be any brake fluid under that switch anyways. So in OP's case here, I think his PO caught brake fluid leaking from that switch and plugged it off. -