Brake dummy light on dash is on

[SKR]

What makes this light come on?

Edited to remove all additional info. All I want to know is what makes this light come on. What switches open or close to put power to that bulb.

[stanski]

Check the emergency brake pedal, be sure its all the way up.

[Palf70Step]

It also comes on with low fluid/pressure.

[TKCR]

It could be the fluid is low or the float is stuck, in the master cylinder.

[SKR]

Removed.

[Redneck Rydes]

Remove the bulb.

[TKCR]

Originally Posted by SKR

I pulled on it hard enough to move the truck, and it doesn't come up any more.





It's got fluid in it. What other symptoms would there be if the pressure was low or the float was stuck? There's no change in the feel of the brakes. Pedal travel is about the same and braking force is about the same as before.

This has been a frustrating summer. Every time I get something done to it, within a week something else is wrong. Sometimes the new problem is related to the old problem, but lots of times it isn't. So I get it back, drive it for a few days and then back into the shop to fix something else.

Google and youtube can be a good place to find answers too. I like Youtube, because you can see exactly what people are describing. There's no doubt something happened when you had your brakes upgraded. Could be that valve, did they bleed the brakes? But I would start out with the simple stuff and work your way to the issue.
https://www.youtube.com/watch?v=CiYnznl2E1w

[Palf70Step]

My guess then is something is shorting out either in you gauges or more than likely something got pinched to where it is putting voltage to that wire (should be a tan w blk strip). Depending on where you disconnected it under the hood, it may be pciking up a voltage on that tan w/Blk wire.

[Bandit130]

Originally Posted by SKR

I had the truck in at the mechanic to fix some oil leaks. One was the valve covers, and the other was the vacuum modulator on the transmission (TH350, if it matters). Since then the light is back on, but the wire is still unplugged. The brakes still work the same as they always have. I step on the pedal and the truck stops.

Check all around the valve covers and vacuum modulator to see if a wire has got pinched under one of them. Could be possible.

[SKR]

Removed. Not interested in anything other than the question in the first post.

[Axle]

Start easy, unplug the parking brake switch (you will see a wire attached to the mechanism, when you set the parking brake, it grounds, turning on the light).

Next, unplug the wire at the brake distribution block on the crossmember behind the rad. Same deal, if the switch grounds, the light lights.

Light go out when you unplug one of those items? Which one? And looking from one of your quotes, you got a little over enthusiastic deleting stuff since it hints at something being unpluged.

Alex.

[TKCR]

Originally Posted by SKR

Removed. Not interested in anything other than the question in the first post.

What make this light come on?

Low brake fluid, or at least the float thinks it's low.
Emergency brake is on. These are the minor things it could be.

Here's something easy to try. On my 01 Honda CRV, my brake light kept coming on and the reservoir was full. So I took the screen out and cleaned it real good and let it dry before putting it back in. The screen had some sediment in the bottom, so I assume it made the float think that it was low on oil. It made the light go out and I never had any issues with the light coming on.
Now I've never seen the inside of our reservoirs, but I'm going to assume they have a screen too. It's worth a shot

[SKR]

I deleted everything because people were getting sidetracked with the other info I added. I was going to get lots of answers why the light could be on, but not how the light could be on. There's a difference, and I can figure out the why if I know the how. So to simplify the answers I took all that out.

So I can check the parking brake switch. The distribution block is unplugged, and has been for a year or so now, so that's not the problem. Is there anything else?

[SKR]

Originally Posted by TKCR

What make this light come on?

Low brake fluid, or at least the float thinks it's low.
Emergency brake is on. These are the minor things it could be.

Here's something easy to try. On my 01 Honda CRV, my brake light kept coming on and the reservoir was full. So I took the screen out and cleaned it real good and let it dry before putting it back in. The screen had some sediment in the bottom, so I assume it made the float think that it was low on oil. It made the light go out and I never had any issues with the light coming on.
Now I've never seen the inside of our reservoirs, but I'm going to assume they have a screen too. It's worth a shot

No, you're not understanding the question (and that's my fault, I can't communicate to save my life).

If the float thinks the level is low, how does it tell the light to turn on? That's what I want to know.

[Palf70Step]

The plastic circuit boards on these dashes are not very good IMO. Something may be causing power & ground to get to that section of the circuit board. Myself, I would just pull the bulb, unless you want to pull the dash and look gor a short/ground issue (big pain)

[TKCR]

Originally Posted by SKR

No, you're not understanding the question (and that's my fault, I can't communicate to save my life).

If the float thinks the level is low, how does it tell the light to turn on? That's what I want to know.

There's a sensor in there.
But something else that makes the brake light come on, is a bad brake switch. The switch is down where the brake pedal is. Or if there is a fuse for the brake light, it might be blown, making the light be stuck open/on.

[SKR]

Originally Posted by Palf70Step

The plastic circuit boards on these dashes are not very good IMO. Something may be causing power & ground to get to that section of the circuit board. Myself, I would just pull the bulb, unless you want to pull the dash and look gor a short/ground issue (big pain)

I like this diagnosis. I don't think there's actually a problem, but it's confusing.

Originally Posted by TKCR

There's a sensor in there.
But something else that makes the brake light come on, is a bad brake switch. The switch is down where the brake pedal is. Or if there is a fuse for the brake light, it might be blown, making the light be stuck open/on.

I must be the dumbest person alive. If there's a sensor in there, how does it communicate with the light? There's no wires or anything coming off the master cylinder. If you follow the lines off the master cylinder they go down to the distribution block or whatever it's called under the radiator. There's a wire there, but it's unplugged. Edit: and it has been unplugged for a year, so its being unplugged isn't the reason for the light to come on.

I still have brake lights, I checked that today.

[TKCR]

Maybe this will help explain it better than I can

There are two switches in the brake warning circuit. If the contacts in either switch are closed, it will create a path to ground and illuminate the BRAKE light on the dash.

One of them is operated by the parking brake lever and closes when the pedal is pressed down (or is hanging down). That is more of a reminder that you need to release the parking brake. If not, you'll wear out your brake pads/shoes and the truck will go really slow.

Now the more serious cause of the BRAKE light coming on:

There are 2 brake lines that exit the master cylinder. Before they lead off to any of the actual brakes they go to the "brake proportioning/combination valve". It is there that the 2 main brake lines from the master cylinder are split into 4 lines. Those four lines then go to the individual wheel cylinders.


https://www.turboimagehost.com/p/175...4x588.jpg.html

There is an electrical switch built into the proportioning valve. The switch is operated by a spool that is normally centered within the valve. If there is a loss of hydraulic pressure on one side of the valve when the brakes are applied the spool shuttles (either the left or right depending on which braking circuit loses pressure), closes the switch and the warning light on the dash illuminates

[SKR]

Originally Posted by TKCR

Now the more serious cause of the BRAKE light coming on:

There are 2 brake lines that exit the master cylinder. Before they lead off to any of the actual brakes they go to the "brake proportioning/combination valve". It is there that the 2 main brake lines from the master cylinder are split into 4 lines. Those four lines then go to the individual wheel cylinders.


https://www.turboimagehost.com/p/175...4x588.jpg.html

There is an electrical switch built into the proportioning valve. The switch is operated by a spool that is normally centered within the valve. If there is a loss of hydraulic pressure on one side of the valve when the brakes are applied the spool shuttles (either the left or right depending on which braking circuit loses pressure), closes the switch and the warning light on the dash illuminates

That's the wire that's unplugged. It was unplugged when the light was off, it's still unplugged now with the light on. The MC can be screaming all kinds of things, but its only line of communication to that light is disconnected. So that's where I was confused - how can that be the cause of the light, if there's no way for it to talk to the light?

[chengny]

Originally Posted by SKR

What makes this light come on?

Edited to remove all additional info. All I want to know is what makes this light come on. What switches open or close to put power to that bulb.

One side of the brake warning light always has power supplied whenever the ignition switch is in RUN (this is also true for the gauges). It comes in on the PNK/BLK 39 circuit.

The brake light illuminates when a path to ground is established on any of the legs of the TAN/WHT 33 circuit. The dwg below illustrates the printed circuit wiring. Red tracer is power and blue is ground:




After leaving the instrument cluster connector the TAN/WHT 33 lead is immediately branched off in two directions. One leg goes straight down to the e-brake switch and the other heads to the main firewall bulkhead connector block:



At the bulkhead connector (on the cab side) a third ground leg is spliced into the one that goes through the firewall - and then out to the brake warning switch. That third leg goes up through the steering column and into the ignition switch.

Most people don't notice but when the key is in the START position, the TAN/WHT 33 is grounded causing the e-brake light to come on (the sensing leg for the coolant temp gauge - DK GRN 35- is also grounded, making the gauge spike full high). Both return to normal when the key is released.



By disconnecting the leads at the e-brake and warning switches, you have eliminated those components. But there is a lot of wiring between them and the brake light. A ground fault in any of those leads will light the dash light. The leg to the ignition switch - and the switch itself - has yet to be tested as well.

If it seems to be in the ignition switch or its associated wiring - I would seriously consider simply cutting the wire at the bulkhead connection - rather than tearing into the column.

[SKR]

Beautiful. Thank you.