Topic: 1967 brake pressure warning light / pressure valve

[Hipo giddyup]

 Well, I reinstalled the rebuilt distribution block and bled all brakes but since I reattached the warning light wire, the brake warning light is still illuminated on the dash. I know I positioned the piston correctly before I inserted the positioning tool that I bought from NPD. Does anyone have any ideas as what could be the cause?  Could there be a grounding issue? Any help would be greatly appreciated .

[midlife]

The bulb and circuitry measures the difference in voltage between RUN-only power and the MC brake signal.  When the MC is grounded, the light will go bright.

What happens when you remove the connector from the MC?  Does the light go out?  No?  Then put the connector back on and remove the voltage regulator plug from the VR.  You may have a bad regulator, a pinched wire somewhere such that the purple/white wire for the MC brake signal is grounded.  You can check for a pinched wire by removing it from the MC and measuring resistance between it and chassis ground.  A pinched wire should be on he order of 1 ohm or less; a good wire should be on the order of kilo-ohms or higher.

[Hipo giddyup]

 Thanks Randy, I removed the wire from the master cylinder distribution block and the light went out. This is where we started from before I even rebuilt the distribution block. I just thought maybe there was a ground somewhere that I missing. I do remember reading where someone said I could slowly bleed one of the rear/front brakes and see if it repositions the pin. That'll be my next step.   

[Brian Conway]

Yeah I bought and used  that ' tool ' and found it useless.  The back and forth balancing and bleeding method works.  Takes two people - read my post again - it's not rocket science.  You'll get it.  Brian   

[67gtasanjose]

The tool is intended to PREVENT the piston of the distribution block from moving during the bleeding procedure. It should only be or have been removed AFTER the brakes are found to be functioning 100% normal. IMHO, there could be no way the piston could have moved to one side or another if this tool was used the way it was intended. Using your image, the 'V" recess in the center of the piston is where the tip is the electric plug sets, preventing the switch from closing to ground. If the piston remained centered during the bleeding process, you should be able to remove the switch and see the "V" notch centered in the hole. (Fluid will not leak out of a properly rebuilt distribution valve). If the piston IS CENTERED, the switch may be at fault. If the valve is NOT centered, the bleeding procedure mentioned earlier will help you (but it still is a PITA to get this centered again this way, especially if working alone or with unskilled help)

[Hipo giddyup]

Thanks for the info. I ABSOLUTELY made sure it was centered, and measured where the V notch would be once I installed the pin back into the block. I then inserted the tool and made it tight enough , it should have been in the notch. There is also NO WAY to look into the block and see the notch , the hole is as small as any brake line hole. I will try to gently let pressure off the brakes , one end at a time, to see if that will work.

I thought about getting another warning light switch but an NOS unit looks to be pricey and not an easy find. I am also unsure if that is absolutely the problem but will consider it if bleeding the brakes does not solve the issue.

[sah62]

I have the piston re-centering procedure described here: https://www.musclecarresearch.com/faq-page#n329

[67350#1242]

I didn't see anywhere in the thread where you checked out the switch.   the brass pin in the end should have spring action when pushed in.  I've seen them stuck closed.   When pushed in there should be continuity between the pin or plunger and the connecting contact.
Of course the contact will be broken when the pin springs back out.
Kurt.

[Hipo giddyup]

 I did not realize that there is a spring within the brake warning light switch. I will remove it and see if the pin can move. How much of a travel are we talking 16th of an inch?

[67350#1242]

I would guess 1/16 to 1/8".   Put an ohmmeter across it and see if it's stuck closed.

[Hipo giddyup]

Sorry, not good with electrical. What should it read?? I do have a multi meter..

[67350#1242]

Zero ohms with plunger pushed in.  Infinity with plunger out.
Use lowest ohm scale on meter.

[Hipo giddyup]

 So I had my meter set on the lower scale. It looks like it was registering  1.  with the plunger not depressed. When I depressed the plunger in it went to 0.00. Does that sound correct? Seems like it is working?

[jwc66k]

So I had my meter set on the lower scale. It looks like it was registering  1.  with the plunger not depressed. When I depressed the plunger in it went to 0.00. Does that sound correct? Seems like it is working?

Yes. Put the tips of the two leads together and you should get 0.0. This is the meter check technique used to verify zero when checking resistance.
Jim

[Brian Conway]

Test the sender just like you would test the door switch/plunger for your int. courtesy lights  Brian