Cool web site and a LED issue.

[adriver]

First go to this web sit and move your arrow around.
Cool, huh?
Sorry, I've just never seen that before.
Playing with LEDs is new to me.
Why do we need resistors in led

This post could go under brakes but since it's an electrical thing.
Anyone had this issue?
I replaced the brake warning light with an LED.
After driving the car with a complete, new brake system the LED started coming on.
The warning switch now has about 3.5K resistance to ground and that is lighting up the LED.
It does not light up an incandescent light.
I'm using a combination valve that I rebuilt I'm wondering what is going on with the valve.
Here. Pretty simple.
1970 - 1976 Mopar Combination Valve Rebuild | Muscle Car Research LLC
Brake action is fine.

Tomorrow I will wack the valve to see if the piston is stuck and almost making contact with the switch.
But if noting changes, I'm thinking I'll add a resistor to the switch wire to make more resistance.
Think that will work?

I'm thinking the switch will still function and the LED will come on as long as the resistor isn't over 3.5K.
(Of course I could just use an incandescent bulb. But the LED is cool.)

 

[Dana67Dart]

Imho... leds are overrated. It is posible that there is always some flow of electricty in the switch but with an incondesant bulb the resistance of the bulb pulls the voltage down to where the light doesn't light. But an LED only needs a tiny amount of voltage so it illuminates.

Just a thought.

 

[pishta]

Stack exchange has that on every one of its pages. I was just there this morning and noticed the same thing. Kinda Tinkerbell but original.

 

[67Dart273]

You may have leakage somewhere. Bear in mind you have two switches to ground in the same circuit........the parking brake switch, and the brake warning pressure switch. I would pull your LED out and check the switch wire to ground, then unhook each switch one at a time, see if one or t' other shoes a resistance. Ideally they should be infinity.

Led's draw very little current, so in some cases it does not take much to activate them. Frankly, if it was me, no more often than the warning lamp is used, I'd just put a bulb in there

So far as a dropping resistor, if you hook a diode--------any diode, or an LED across a battery and you get the polarity such that the diode does not conduct, or "reverse biased" then nothing at all happens

If you hook an LED the opposite way to a battery so that it conducts, it is "forward biased" and for easy explanation, acts then as a DEAD SHORT, so the diode fails.

So you need a resistor to limit current flow to below that of the diode's rating

 

[RedFish]

You state that the switch has little to no resistance to ground... its closed. Either type bulb would be on.
Factory service manuals state that proportion valves are not serviceable. No kits or how tos from them. Their service techs trained to rebuild transmissions, carburetors, etc,, but not these brake valves? That's something to ponder. Good luck with it.

 

[67Dart273]

My own opinion, but that brake warning switch doesn't tell you a thing that your foot (on the brake) won't already have told you..........."We have a problem"

 

[adriver]

I hear you, Dell.
It's an idiot light.
I'm doing for someone else and I'm crossing all the eyes and dotting all the Tees.

The parking brake isn't in the circuit I'm testing.
This quick disconnect in the picture goes down to the switch.
I installed it for investigating this.
Easier than crawling under.


OK. I'm obviously going to have to do some more work on this and get the car hot again.
I wanted to call in the better minds and see if anyone else has run into this.

Went out today, cold car.
Checked. Pump brakes nothing changed.
Reading right off the switch at my connector on the fender.
All good.

I've got to start not relying on my memory so much and write things down.
I'm not being very precise.

When I parked the car Saturday it was hot and I THINK the reading was
about 1/3 meg.
Could have been 3.5 K or .3 M but the switch did NOT light a incandescent test light, regardless. It was supper time.
And it WAS making the LED bulb come on.
BA9s LED Boat and RV Light Bulb - 4 LED - BA9s Retrofit | Super Bright LEDs

What I'm wondering now is the conductivity of the brake fluid.
Maybe that's entering into it.
To be continued.

 

[adriver]

Very interesting.
To confirm previous..
Took car out and got it hot.
Riding along and the LED started coming on.
Not under actual time of "braking".
Suspect resistance in switch dropped to previously reported 3.5K under mixed driving.
Got home and checked resistance through switch to ground..
Findings.

Test Light DID NOT illuminate with this reading.
(Positive light feed to switch resistance)

Good test light.

Valve on this car was cleaned and serviced and not the first one I've done.
Not rocket science.

NOW, the next thing to check is another car with the same type valve and NOT an LED and see if it's comparable to this switch.
I'm thinking a resistor is to way to go since a "new" valve might do the same thing and it's a PITA to change.
OR I could just use a 57 bulb and it would not light.....I guess.

To be continued.

 

[adriver]

I've looked at some brake threads for master cylinder info and figured I would throw this out there too.


The car had good brakes with this build.
No complaints except for the nuisance warning light.
This is a B body with manual brakes.
But I'm curious why it is doing this.
Checked one of my A bodies with the same brake system (valve,etc) and it was "out of limits" with the Fluke after being driven hot.

(The A body is still using a
Raybestos MC36412 master cylinder)
So I'm thinking a drop in resistance I'm seeing in my B body valve/switch isn't normal.

I have installed a new A body valve (not rebuilt) from Inlinetube just to see what happens.
I'm using a Diplomat master cylinder on the B body with the 2 bolt adapter.
It has a 1.031 bore.
Again, bolted right in with the adapter and the brakes worked fine.
Stock rod was good.
This master cylinder is aluminum and was new when installed 5 years ago.
(Problem here?)
It has the same fitting sizes as the A bodies original master cylinder.
9/16 20 and 1/2 20.
(Don't want to make new lines./fittings . I did that once already)
Front calipers are Diplomat.
The rear drum cylinder are 15/16.. 10 inch drums.
(WCA 78734)
Need to bleed them and recheck but I'm thinking it will be the same result.
Something will move and "make" the switch enough to cause the LED warning light to come on.
Seems to come on about 5.7 K resistance.

These are just links to the master cylinder I'm using on the B body.
https://www.autozone.com/brakes-and...ster-cylinder-brake-system/49330_101749_2558#

https://www.oreillyauto.com/detail/...0/1988/dodge/diplomat?q=master+cylinder&pos=1

Brake Master Cylinder-First Stop Dorman M99294 82702402375 | eBay

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