I have installed power brakes with disc brakes on the front and drum brakes on the rear on my 1966 F100 2wd. I did install a combination valve. I am wanting to wire the brake system warning light. A single wire sensor came with my combination valve, so I was planning on wiring it up like a 1967 F100. I found a wiring diagram for the 1967. It shows the the wire from the sensor going to the ignition switch on a side tab. I have the correct ignition switch to install. From there it goes to the indicator light. I plan on installing that in place of the lighter. I don't smoke and mine is already broken. From there the diagram shows a wire from the indicator light splicing into the red-green stripe wire from the ignition switch to the ignition coil.

I have a couple of questions. Can anyone explain to me why this needs to be hooked up to the ignition coil? Is it necessary to hook up it up to the ignition coil? If not, can I just ground that wire. I am assuming that the wiring set up gets it power from its attachment to the ignition switch. Maybe that is wrong.

Thanks,
Rick

 

Maybe I’m ignorant, but to my knowledge there is no brake warning light on a 66 pickup. I have two 66 pickups and they only have three lights in the instrument cluster; oil psi warning, low charge warning, and hi beam indicator.

 

There isn't. I am wanting to add it. I have added a combination valve that allows me to add it.

 

Okay, now I understand. Reference a shop manual for the year the combination valve came from to get the conditions that trigger the sending unit to complete the circuit to the brake warning light. Maybe it completes a ground, maybe it sends voltage. There should be something in the manual - maybe a basic explanation of operation or in a trouble shoot section.

 

Good idea. I will try to find one. Thanks.

 

You should probably check it with a volt meter, but I'm pretty sure the warning switch provides the ground. The red wire with green stripe provides the power, probably switched power. So you could use any similar switched source, it doesn't need to involve the coil.

 

Could I use the accessory peg on the back of the ignition switch or even the old power wire for the lighter as a power source?

 

I dont see the need for this light because when it comes on the pedal goes to the floor, that right there tells me something is wrong!
Nothing other than a tach wire should go to the coil.
I also would not use the lighter hot wire as it is hot all the time.

You should be able to find a hot with key on in the fuse box.
As said the switch grounds when there is a brake issue.
Fused power with key on> light> switch
Dave ----

ps what side of the coil did the wiring go to?
I ask because when the key is first turned on the light should come on for a few seconds to show the bulb works.
I dont know how this is wired for this to happen so wonder if that is why the coil wiring?
My way above would not test the bulb.

 

Thanks. I don't know which side. I am only looking at a diagram. It shows it to be before the resistor wire. I suppose it hooks onto the wire either at the ignition switch or somewhere underneath the dash. As I have been thinking about, what is the purpose of the wire going to the separate post on the ignition switch? Could this allow the light to come on when starting? I had not thought about the lighter wire being hot all of the time. Good point. I think that I will wire it so that it only works when the ignition is on. If that does not work, then I will tap into the wire going to the coil Thanks.

 

If it is on the IGN. switch before the resister wire then I dont see any issues with it there.
When you said "coil" I was thinking out "at" the coil and why I said nothing gets hooked to it.

I think it has to be there for the bulb test before starting other wise how would you know if it worked or not?
Again when it comes on the pedal goes to the floor and I dont know how you could miss that and need a light to tell you something is wrong
Now that I think of it my light does not come on as a test (81 F100 flare side) but my seat belt light does work.
I also have LED bulbs in my cluster so wonder if that bulb is in backwards? I have to fix 2 others so I will have to look into that. (thanks for giving me more work LOL)
Dave ----

 

I now have a dual chambered master cylinder. If, for example, the rear fails and the front does not, will the pedal still go to the floor? I was thinking that it wouldn't, so I thought hooking up the warning light would add safety.

Sorry for adding to your work. All I seem to do is more to mine.

Thanks,
Rick

 

Yes if you loose 1 side of the dual brake system the pedal drops vary low just feel like to the floor!
But you still have that 2nd system to to stop with.
When you added the new dual master and was bleeding the brakes when you opened 1 part of the system the pedal dropped down low but not really to the floor, its the same way.
Dave ----

 

Light is super simple to hook up, let's not complicate this any more.
1) the contact at the combo valve grounds.
2) the light at the dash must be isolated from ground.
3) switched positive to one side of the light, the other to the combo valve.
You're done.

 

Thanks. Can I get the positive from the accessory post on the ignition switch or would you recommend somewhere else.

 

I finally got this brake warning light wired up. As said in this thread, this is not absolutely necessary, but Ford started to install them in 1967 for safety. Starting in 1967 Ford went to a dual chambered master cylinder, one for the front and one for the rear. And with that they started utilizing a brake pressure differential valve. If the front or rear brakes loose pressure, the valve moves closer to that side and a sensor attached to the valve is grounded, completing the circuit with the brake warning light coming on.

Starting in 1973, Ford starting routinely installing front disc brakes with drum brakes on the rear. You could get them earlier than 1973, but it did not use a proportioning valve, which decreases the pressure to the rear brakes during a hard stop to try to prevent them from locking up. The proportioning valve was incorporated with the brake pressure differential valve and the metering valve, which is referred to as a combination valve. Sometimes inappropriately just called a proportioning valve.

In 1967 it used a single wire to the sensor to the brake pressure differential valve. Starting in 1968 it started using a dual wire sensor. Because of this it has been said that the brake warning light in the 1967 will not light up during starting to let you know the bulb is still working. I believe this is wrong and I will explain later why.

As I have said, I added disc brakes to the front of the my 1966 F100 and redid the rear drum brakes. I added power brakes booster that now has a dual master cylinder. Because of this conversion, I elected to add a combination valve. My combination valve came with a single wire sensor. All you need for the brake warning light to work to signal that the brake pressure differential valve has been tripped is a power source. This can be any power source. You could use the accessory peg on the back of the ignition switch for this. But the warning light will not come on during starting to indicate that the light bulb is working.

The 1967 wiring diagram shows that the positive wire to the warning light is spliced into the wire from the ignition switch to the coil. This allows a positive electrical source with the ignition in the on position and as well as in the starting position. When you purchase a replacement ignition switch for a 1965-66, what you get is an ignition switch for a 1967. It looks the same, but it has a tab on the side that is for the brake warning light. What I think this does, and someone can correct me if I am wrong, is function a ground when the ignition switch is in the start position, thus completing the circuit and allowing the light to come on during starting. My light will come on during starting of my truck. It goes off after it has started, indicating to me that my brake pressure differential valve has not been tripped. I can test this by grounding my sensor on the combination valve artificially and see if the light comes on in the on position. I have not done this yet.

I took a wire from the combination valve sensor up into the cab. A wire from the side tab on my ignition switch. And one of the wires to my brake warning light. Using a three-way connector, I tied these three wires together. The other wire to the brake warning light I spliced into the wire from the ignition switch to the coil. And because I have used an new replacement ignition switch with a brake warning tab, a combination valve with a sensor for the brake pressure differential valve, and wired it the way that I did; my brake warning light will come when the ignition is in the start position.

I searched numerous threads for hours trying to understand this and stared at the wiring diagrams for additional hours to finally come up with what I think is how it works. Hopefully this is helpful to someone.