Brake light on dash

Besides engaging the parking brake which activates the brake light on the dash, what else would activate it?

I took the 68 out for a drive tonight since there was no rain and the roads were nice. I was ahem “testing” my “new” wheels out burning some rubber and then randomly the brake light switched on. Now it glows but not a full bright glow like when I active the parking brake. Now its just a dimly lit at all times with no brake engaged. I rechecked the bulb and also the connection at the prop valve. Couldn’t find anything in the chassis manual about it either. This is probably something very simply but Im not sure. Thanks in advance

 

Other things to check, wheel cylinders and all fittings for leakage and lines for pinholes as well as the master cylinder level.
Crack the bleeders and see the condition of the brake fluid.

Internal/eternal leaks, air, water, plugged lines, sticking/leaking wheel cylinders faulty MC differential pressure spool can all lead to the light.

Not knowing how long it has been with any and what type brake servicing, we're guessing.

 

Thanks for the reply’s everybody I figured the culprit out, and embarrassed to say, but the reservoir was simply low. Which I just realized there is very slow leak which I found to be around/behind the cap dripping down the MC. A few months ago I replaced all the lines/master cylinder/brake booster/wheel cylinders/prop valve. No other leaks in the system except around the cap. I also verified all the fittings throughout the system. Other than that the brakes work perfect. But I am now assuming the new cap is just bad? It’s not original cap, bought it from inline. I will try using the old one after I clean it up a bit.

 

The connection that screws into the dist block where the tan wire connects to was loose. Screwed it down and the light is a lot dimmer rather. That connection might be stripped because it just keeps spinning.

 

Just kept tightening, its off now. But Cap still leaking, will have to address that.

 

Check the cap rubber seal/bellows and see if it has gotten soft. Some rubber is cheap, reacts poorly to some brake fluids.
Also cleaning the top sealing area on the reservoir in case some gunk is on it.

Some folks will use a thin film of fluid on the sealing areas of both, and some will make sure they are clean and dry.
The spring bales that hold the cap can also be bent and too loose.

 

Hope it is the nylon type that is mangled.

 

Very interesting. Just got back from driving around— yea its just dimly lit, Ill post some pics in a bit, activating the parking brake then turns it on completely. But playing with the distribution block connection makes it dim, very strange. I bet its the cheap part, since it it loose just spinning freely. 68 skylark custom

 

If the parking brake set (or that switch is the issue) the light is bright.
If the brake pressure and/or switch is the cause, the light will be dim. (certain on the '68)
By design.

(and why I posted all that mess about lines and stuff, because srobinr mentioned the light was dim)

 

Could have a high resistance ground that changes when you wiggle it. That would allow a "dim" light.

 

I think the parking brake switch sees a lot more action then the distribution block switch. The distribution block switch is probably just corroded/ dirty so it doesn't make as good a connection, hence the dim light.

I agree with Jason, I don't think this is by design. It's on or off... I am all 1968 too.

When you say it's leaking from the cap, you mean the lid right? Not the back of the cylinder where there is a rubber boot?

 

All this happened right after I removed the dash to inspect wires/clean and install LED bulbs, I repaired some wires that were frayed and old(4 of the wires from ignition switch, purple/green/pink/red)- installed a new ignition switch and also a glove box tumbler/lock.

Currently the ash tray light will not work with any bulb I tried, as well as trying reversing polarity as well. (The ash tray light wasn’t working before anyways)

The glove box lock has a bulb that was acting up, the interior lights not shutting off when i closed the door and the ignition switch was not starting at all but had power to light up everything- I had to move glovebox bulb around in the socket until everything worked again. (There wasn’t a bulb in the glovebox light before either)

And yes the cap is leaking, here are some pics you can see drips from the actual cap and also the fluid eating up the paint of the MC.
Also are pics of the dash with off, on, and parking brake engaged.

 

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Jason/Max D, I stand corrected on the dim/bright brake warning light bit.

I just went out, pulled and Ohmed the switch and then tested it by grounding/pressing it and it is the same level as when the Parking Brake switch is used.


I had replaced all my lights except headlights with LEDs, I had trouble with the front turn signal, brake warning and glove box. The glove box was polarity issue, so I put in a "dual path" LED and fixed that. (More on this below).

The front turn signal bulbs would not work, even when I switched out both the turn flasher and the four way flasher with digital made for LED versions, so I put incandescent back in and put it on the "low priority to do list".

I also had the issue of the brake warning light being always on, about half level of the light when the Parking Brake pedal was pressed.
If I pressed the Parking Brake it would fully illuminate.

After swapping another LED in the warning lights that worked correctly, and seeing the one the "problem" did not move with the bulb, I changed the pressure warning switch (had another one on the bench from a bad combo valve) and it still was illuminated, (dim), I put the incandescent back in and the warning light went out. I was also doing brake bleed so I did not bother with putting the LED back in and trying to find the reason for it always being on. (Now I want to know why the LED is always on when it is installed...)

Later (and my brain) settled on the switches providing to levels of illumination as a function, I assumed it was either a resistor in the switch on the combo valve or the resistance of of the switch grounding through the valve spool/bore that was enough to result in two brightness levels and left it as "fact". (I have had vehicles that do have two levels for different issues with brakes/Parking Brake on and simply believed it was the same with my '68)

Or it's that Mandella Effect thing, so if I can blame him, that's my story.


The glove box light on some year models (I don't know the years, but 64-65 and 68 I do know) are "powered" through the base/cap, and "grounded" through the foot/contact, in reverse of all the other bulbs, so a (single diode or one way flow if multiple diodes) LED bulb being circuit polarity specific will not work, and needs to be a "non-polarity" LED (basically two LED in parallel with one having flow in one direction, and the other facing 180) in a single bulb.

Any (DC) bulb circuit in a car that is opposite (power through the foot/contact and ground to the base/cap as typical) current flow, will need a "non-polarity" (term people use), is actually twin LED in the bulb that lights one LED in one direction, and the other LED by current flow in the other direction. (and this is simpler than using a bridge rectifier).

As the cost of LED (for DC use) packages become cheaper to make, the use of dual LED packages is becoming the norm so the end user does not have to deal with the issues and can simply put a bulb in and it works.


/drift