Brake Light switch

[iviper123]

i am having trouble with my brake lights now working all the time when i press the brake, does some one have a wire diagram for the switch? everything elese works just not the brake lights, so the switch sould still be good? i have no trouble getting out of park or shutting of the cruise by tapping the peddle, i need to find out which wire is for the brake lights.

 

[FellowTraveler]

Check the hydro-boost could be defective is it leaking, or?, if so maybe the brake pedal is not fully returning.

The brake switch is attached to the pedal w/spring clip which more likely than not will break when you try to remove it.

 

[schiker]

Still could be the brake switch contacts are worn or burnt. The cruise cut off is probably a "digital" signal no real current.

I don't know for sure but think the park safety is a pressure sensor. I know some cars I have to pump the pedal to build a little more pressure occasionally to get out of park.

So those tests might not prove the switch is good.

If you do try and isolate the brake light wire measure current or use a test bulb not just try and measure 12v.

 

[JayTheCPA]

i am having trouble with my brake lights now working all the time when i press the brake . . .

Am confused, are the lights 'On' all the time, or not working at all?

If they are not working at all, at the risk of insulting . . . Are the light bulbs still good?

Reason for the question is that given the cruise reacts to the brake pedal, we at least know current is going into and out of the brake switch. Naturally this does not mean that the switch is out of play yet, but it is at least partially functional.

Seeing as a 98 is OBDII, an easy and non-invasive way to tell whether current is going to the brake lights is to look under the dash (above your left foot by the e-brake) for a panel with an empty "NAT" plug (the same port to trigger a brake controller); if a multi-meter shows good current (ex ~13v and not under 12v) when pressing the brake pedal and the bulbs are good, I'd focus on wiring to the lights and start at the harness in the rear bumper.


If the lights are 'On' all of the time, then it is likely just the switch (as suspected).

 

[FellowTraveler]

Another are to look is the emergency flasher circuit which if defective, not fully reset or it wiggles can prevent brake lights from working.

Hydroboost diagnoses for no or intermittent brake pedal return can be found on web.

 

[WarWagon]

X2 on checking the pedal return height. However if the cruise is cutting out I suggest adjustment or height isn't the issue.
Note: The brake switch has a lever on it that allows for adjustment.
IMO brake switches fail often and tend to stick the lights on when they fail. Last one on my 1992 project didn't light up at all from burnt contacts.

IF anything I would throw a switch at it... One of the few parts I throw parts at first...

 

[THEFERMANATOR]

The 95+ trucks use a COMPLETELY different switch than 94- trucks did. It is NOT adjusteable as it simply goes over the brake pedal pivot point and is spring loaded. It takes about 2-3 pounds of pedal pressure to push the spring in the switch and make contact inside the brake pedal switch. The brake pedal switch is a 3 part switch with 3 SEPERATE sets of contacts inside of it. You have one set of normally closed contacts in it for the shift interlock solenoid(the switch that prevents you from shifting until you depress the brake pedal). It powers the soelnoid preventing it from allowing the shift cable to move, but once you depress the brake pedal it cuts power to it. Next you have a set of normally closed points which sends power to the ECM when the brakes are not pressed. Then you have a set of of normally open points that are powered when the pedal is depressed. This set of points is the ones that actually turn on the brake lights, but it also sends a signal to the ABS and ECM. EITHER set of ECM feeds can cut the cruise control as it is a double fail safe system. Also the power to the normally open set of points that powers the brake lights also powers the turn signals, so if they're working the brake switch should have power to it. And don't automatically assume the switch is faulty because you have no brake lights. Not sure if your truck has the 3rd center high mount brake light, but the brake/turn signal lights run ALL power through the multifunction turn signal switch. So if theres a problem in your turn signal switch, you can lose brake lights. Give me some time, and I'll find the wiring diagrams for the brake switch and post em up.

 

[THEFERMANATOR]

From what I can find(all I have is my 95's diagrams, so the wire colors may be different from OBD1 to OBD2, but they are both the same body style so should be very similiar as far as wiring goes), the orange wire to the brake switch is the power feed from the fuse panel for the stop lamps, and the white wire is the wire that should carry the brake light's power from the switch. This wire goes to the turn signal switch, and it sends the current back to the rear tail lights. If you have a center high mount stop lamp(3rd brake light), it will be powered off of a splice in the white wire BEFORE it goes to the turn signal switch.

This is a picture of the brake light jumper harness connector. Theres about a 6 inch or so long harness that plugs into the actual switch, and this is the connector that hooks to the body harness. It is reccomended to do all testing at this connector instead of the actual brake light switch. From what I can find, this is what each wire should be. I'm not putting which cavity each should be as there is conflicting info as to which is which for the C, D, E, and F, but A and B seem to be for the brake lights in everything I can find.
orange is 15 amp power supply for brake lights
white is brake light power out of switch to truck. Goes to a splice point where it branches off to turn signal switch, ECM, ABS, and 3rd brake light
purple is the ECM feed for the normally closed side
brown is the power for the normally closed ecm feed
green is power to the switch for the shift interlock solenoid
green white stripe is power to the shift interlock solenoid