Topic: 1967 Brake Indicator Light on Dash

[midlife]

I'm trying to figure out a reason for Ford putting a spade lug on the outside of the ignition switch for the brake indicator light.  There are two wires there: one goes to the dash, and the other out past the firewall to the single wire sensor on the master cylinder.  The dash wire goes to a bulb, which gets power from the other side of the bulb from a wire that is only hot when the key is in the RUN position.

Does power go through the spade lug on the ignition switch with a position of the key?  There is no clear documentation in all of the schematics I have.  I don't have an owner's manual to look up if the brake indicator light lights up with a certain key position, for example, when starting the car.  I do not have a 1967 car at my disposal to check.

Can someone help me determine if this light can only come on when the MC is locked up or is there another way to get the light to function?

Thanks in advance.

[ruppstang]

Midlife,
I just checked my 67 the light does not light in any switch position.
The owners manual states
Thisis a stand-by safety feature. Light will never glow when the engine is running unless a leak develops in the dual hydraulic brake syestem.
Hope this helps. Marty

[jwc66k]

I think that the federal government mandates on the dual master cylinder system included a test of the warning light. I tried following the wiring in the 67 Electrical Assembly Manual but the pages are too cumbersom to follow, even sober. There is a lot of extra wires so I would assume there is a lamp test when the ignition key is in the start position. The light is activated when one section of the master cylinder is low and the actuation rod in the distribution block is forced to lhe low side. Why it was forced would be low fluid caused by normal use (and the operator/owner not checking fluid levels), a catastrophic brake system failure, or, as previoulsy mentioned, a slow leak.
Jim

[midlife]

I gotta think Jim is right, because the two wire spade connector at the ignition switch is there for a reason.  If it is simply to allow two wires to be joined, why not go with one wire and be done with it?  If the spade lug is not hot at any time, why put it on the ignition switch? 

The power to the light comes from the red/green wire on the ignition plug to one side of the bulb; the other side of the bulb goes to this spade lead and another wire goes out to the sensor switch.  I can't fathom a position of the key that would power up the spade lead to work the bulb unless it was ACC only and the sensor was showing bad brakes.  Maybe that's it...a way to check the MC position without keying up the coil and points.  Hmmmm...

I'm getting a new switch (repro) and intend to test it.  My current switch broke the ACC post, and it may have inadvertently applied power to the spade lead, because the wire to the sensor completely fried itself (MC was shunted so the sensor was grounded).

[ruppstang]

Tonight I went out to the garage and checked a 68. No light test out in any switch position on that car either.

[Murf]

Randy, I think the circuit you are pondering was called a "PROVE" circuit and was common on most ford products of that era.  It was meant to be a primative type of a self check for the ability of the fail feature of the dash.  Also seem to remember that you had to turn the ignition switch very slowly from off to start and the prove light would go on for just a tiny time frame when the ign switch passed between "on" and "start".  One hardly noticed the light under normal circumstances.  Just my memory of things that happened during that period in automotive development.  Nobody really paid much attention to this feature and most did not know it was there.  Someone else may remember it differently.

[midlife]

Randy, I think the circuit you are pondering was called a "PROVE" circuit and was common on most ford products of that era.  It was meant to be a primative type of a self check for the ability of the fail feature of the dash.  Also seem to remember that you had to turn the ignition switch very slowly from off to start and the prove light would go on for just a tiny time frame when the ign switch passed between "on" and "start".  One hardly noticed the light under normal circumstances.  Just my memory of things that happened during that period in automotive development.  Nobody really paid much attention to this feature and most did not know it was there.  Someone else may remember it differently.

Ding ding*  We have a winner! 

I took the switch apart and yes, there is a lead from the external spade lead to the internal guts of the switch.  Unfortunately, my switch has the ACC post broken off, but we could see what was going on.  There is one point where the guts press down on a tiny bit of metal to make contact to the external spade lug, and we surmised it was during the CRANK position. 

What happened was that a client's harness burned up from the spade lug out through the firewall to the MC sensor switch via the violet wire.  The sensor is good (reads different resistance if it is plunged or not) and is grounded when the plunger is engaged.  So...his MC was not balanced, and when the ignition switch broke, a piece got entangled with the guts forcing power out to the sensor bypassing the normal bulb that is in series with the sensor.  And...with a full 12V going to a grounded sensor, the wire got hot and melted the insulation.

[ruppstang]

Randy, I think the circuit you are pondering was called a "PROVE" circuit and was common on most ford products of that era.  It was meant to be a primative type of a self check for the ability of the fail feature of the dash.  Also seem to remember that you had to turn the ignition switch very slowly from off to start and the prove light would go on for just a tiny time frame when the ign switch passed between "on" and "start".  One hardly noticed the light under normal circumstances.  Just my memory of things that happened during that period in automotive development.  Nobody really paid much attention to this feature and most did not know it was there.  Someone else may remember it differently.

Yes that makes sense how it should work. I wonder if that contact in the ignition switch could wear and not make contact. It does not seem to work in any of our cars. One 67 has the low fuel light and it has a prove out that works on it.

[RocketScientist]

I am curious to know if the repo switches have the same arrangement or if its one of those small things they have forgotten to replicate.
Brad.

[midlife]

I am curious to know if the repo switches have the same arrangement or if its one of those small things they have forgotten to replicate.
Brad.

I'm expecting a repro switch from VA Classic momentarily and will report what I find.  I believe the switch I took apart was repro.

[midlife]

Update:
I got the repro ignition switch and transferred the tumbler guts over to it.  I thoroughly rung the ignition switch out and DID NOT get the external spade lug to register any voltage or continuity to any of the other 3 contacts.

Hmmm.  I know Ford began using proof-out circuits about this time and I'm willing to bet there is a difference in ignition switch internals for other models that does use this feature but not the Mustang for 1967.  However, the ignition switch I did tear apart certainly does have the external spade lead going into the interior of the ignition switch in a non-simple way that interfaces with the rotating disk.  A different rotating disk MAY get the external spade lug to work for the proof-out circuit.  This may have been a cost-savings measure to keep the external part of the ignition switch the same.

[ruppstang]

Randy I got out my 67 Ford electrical manual to night and it shows no wire going to that spade. The big fords used it for the hot temp light. The wire # is 641 and it shows that the spade goes to ground internally in the switch. If you ever need the Ford full size drawing I have the 66, 67 and 68.
Marty

[midlife]

Yeah, I'd like to see it.  I know from taking the ignition apart, there was an insulated sheet separating the tab from a hot plate in the normal configuration.  When the rotor turned to the unique position, the tab would press downwards and contact something hot.  Perhaps the rotor design was such that the tab never moved.  When the switch's ACC post broke, small pieces of plastic got entrained in the mechanism and that is what caused that spade lug to go hot.

I suspect the design intent was as you say, but it was not fail-safe.

[jpwatkins9]

My 67 GT has the original ignition switch, when going from off to crank, all of the warning lights test (go on) and then go off  when the engine starts (key released from crank position).  This is to test all lights when starting the car.  Have had it since new, so not a repro switch.

John

[67gta289]

I checked two and in both cases, the subject spade terminal was isolated in every key position except crank.

At crank, there was no electrical connection to any other terminal.

However, there WAS a connection to the housing itself, which would be grounded when installed.

Since the sensor has a single wire, when brake fluid level is low, and the spool shifts fore or aft, it grounds the circuit.

This all makes perfect sense to me.  Anyone else?

As for the wiring diagrams, I have the full (2" thick) 11x17 wiring diagrams for all Ford vehicles, including large trucks.  There is no brake level indicator circuit to be found.  If someone has it, I would like a copy!