Topic: 1967 Brake Indicator Light on Dash

[67gtasanjose]

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!

DING DING, we have a winner! I knew this one all along when it was brought up about 6 weeks ago in another thread but did not wish to go prove it out. Think about it...It CANNOT GO TO POWER because if there IS a brake failure, the switch at the distribution block would cause a short circuit.

Thanks John for putting this to rest for those who were not sure. YES, there SHOULD be a prove-out lamp of the brake lamp, it requires a properly grounded and GOOD ignition switch.

[1967 eight barrel]

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.

The prove circuit for the low fuel lamp is not powered by the ignition switch, but the lead that runs from the starter solenoid  to the male red wire that exits the firewall.

[67gta289]

The prove circuit for the low fuel lamp is not powered by the ignition switch, but the lead that runs from the starter solenoid  to the male red wire that exits the firewall.

Correct - but the topic here is the "brake" lamp on the instrument cluster that indicates a low brake fluid level.

[67gtasanjose]

IN SUMMARY:

Randy, I think the circuit you are pondering was called a "PROVE" circuit... CORRECT

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.   CORRECT

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.  Partially CORRECT. The low fuel prove out is 100% seperate, connects to the solenoid as eight barrel points out

The prove circuit for the low fuel lamp is not powered by the ignition switch, but the lead that runs from the starter solenoid  to the male red wire that exits the firewall.  CORRECT

Correct - but the topic here is the "brake" lamp on the instrument cluster that indicates a low brake fluid level. CORRECT, but mentioned earlier and may, by mentioning again, cause some confusion

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

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

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

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

This all makes perfect sense to me.  Anyone else?   CORRECT, all along...was waiting for another to prove it out

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.... CORRECT. I understand some foreign countries required this to be added onto Export examples before allowing them

DING DING, we have a (another) winner! I knew this one all along when it was brought up about 6 weeks ago in another thread but did not wish to go prove it out. Think about it...It CANNOT GO TO POWER because if there IS a brake failure, the switch at the distribution block would cause a short circuit.

FWIW, I just tested out my USA made Repro Switch and it functions as John (67gta289) described, the spade connector grounds out to the case when turned to "start" position. I could check my other USED switches too, but believe it to be a mute point at this time.

Bottom line, YES...It IS A PROVE-OUT circuit for the BRAKE failure warning lamp and also, it is not to be confused/combined in function with any other "lamp test" on the vehicle (including the "low fuel" lamp/prove-out test).

[jpwatkins9]

John,  exactly, when in the crank position, the spade lug is grounded through the body of the ignition switch grounding the lights on the instrument panel as a light test.  For the dual brake proportional valve, the wire to that should have 12 volts on it through the warning light bulb.  When something goes bad on one of the brake systems, the shuttle moves and grounds that side of the brake warning warning light and the light turns on.  Easy to check with a voltmeter or just a wire.  Ground the wire going to the switch and the light should turn on.