The brake switch has 4 terminals. One pair is closed when the pedal is depressed. The other pair is closed when it's not. I think there's a term for this, like "double-pole, single-throw" or something. Anyway, what does closing the 2nd pair (brake pedal *not* depressed) do?

 

the switch is not a relay....

 

Purely a guess but, cruise control cutoff?

 

Either cruise control cutoff, or on an automatic car, the system that locks the selector in Park unless you press the brake. Though on the Civic I think that system works through the brake light circuit.

 

Cruise control

 

Cruise control. Definitely.

 

what you have is a single actuated 2xSPST, one NO one NC. [Single Pole Single Throw, Normally Open, Normally Closed]
and to put this to bed... as stated the second set of contacts are for the Cruise Control option.

 

I was thinking that depressing the brake pedal closes the NO contacts, deactivating cruise, turning on the brake lights and activating the shift solenoid allowing the shifter to be moved out of "park".

Are you saying that cruise is actually deactivated by the NC contacts getting opened when the brake pedal is depressed? Maybe because that simplifies the cruise circuit? That does make sense.

I checked continuity on the switch. NO is fine but NC has very high (~1M ohms) resistance. I'll have to double-check cruise, which worked last time I used it. The reason I'm doing this is because my brake lights stopped turning on. I'm currently confused because the brake circuit (NO) is fine while the *other* one seems to have the problem. Argh.

 

When the cruise control switch is pushed to ON, power is provided to the cruise control unit and the brake switch through the normally closed brake switch contacts.

The brake switch releases the system’s control of the throttle at the instant you press on the brake pedal. The switch sends a signal to the control unit by removing power from the normally closed brake input (GRY wire), and providing power at the normally open brake input (GRN/WHT wire). The control unit responds by allowing the throttle to close. The clutch switch or the A/T gear position switch sends a “disengage” signal to the control unit that also allows the throttle to close.

 

So the "signal" sent to the cruise control unit consists of a loss of power from, or through, the NC brake switch contacts? I wonder why the cruise control's power isn't simply routed through the NC brake switch contacts? Because the cruise control has to receive a signal in order to perform other functions like releasing the throttle? Still... Why not give it the signal by closing the NO brake switch contacts? I still don't get the point for the extra pair of contacts. Why can't the same job be done with only a single pair of (NO) contacts?

And why, when it receives the signal from the brake switch, does the cruise control then provide power to the NC contacts? Is that power used for some other purpose?

 

WHY??? BECAUSE THATS HOW THE MOTHERF-CKING THING IS DESIGNED!

 

hope you're not trying to tap it as a power source...

 

It likely is possible to just use one pair of brake switch contacts. However, using both the NO and NC contacts from the brake switch probably works as redundant safety signals from the brake switch to the cruise control unit to allow the throttle to close.

When the brake pedal is depressed, power is removed from the brake switch NC contacts.


More Info:
Here is a little more information. There are 3 switches referred here: Cruise control main switch, Set/resume switch, and Brake pedal switch.

When the cruise control main switch is pushed to ON, power is provided to the cruise control unit and the brake switch through the normally closed brake switch contacts (from the cruise control main switch there are two separate power inputs wires that feed the cruise control unit when main switch is ON).

With cruise control activated, when you depress the brake pedal, the brake switch releases the system’s control of the throttle at the instant you press on the brake pedal. The brake switch sends a signal to the control unit by removing power from the normally closed brake input (gray wire), so that the control unit responds by allowing the throttle to close. (Depressing the brake pedal only removes power from the normally closed brake switch wire to the cruise control unit; but, not the power from the other wire from the cruise control main switch when it is ON.)

You can cancel the cruise control system by turning the cruise control main switch off. This removes power to the control unit and erases the set speed from memory. If the system is disengaged temporarily by the brake switch, or clutch switch, and the car’s speed is still above 25 mph, pressing the resume switch will allow the car to automatically return to the previously set speed.

Honda’s brake switch is also used in part to allow for the cruise control system to resume the previously set speed without erasing the set speed from memory.

You're chasing a rabbit down the hole (cruise control) when the issue is the brake lights.

 

Most cars have 2 brake switches, or a really over built and gaudy single switch with 2 switches in it.

I'm sure there is some federal law about the engineering of the switch

 

I know it might seem like I'm belaboring the point. But I feel much better when understanding the whys and wherefores. And satisfying my damned curiosity. LOL.