Bad brake switch under dash

GNRick

Retired member
Interesting....your switch looks nothing like mine. You have 6 wires and I have 5 wires. If you search for the 1987 brake switch on rock auto, the switch that is used in my car comes up.....http://www.rockauto.com/catalog/catalog.php
It is part # 25523463. The non GM switch will work, but the connections are in a different place. I know this because I bought one from Oreillys and also one from Advance. They are black in color, while the GM switch is white. The blue connector with the two wires plugs into this switch, and another connector with the three wires also plugs into this switch. Are you sure your switch is stock? Also, my transmission used to lock up, but then it quit. HOWEVER, if you energize the brown wire at the transmission, and ground the tan/black wire, it DOES lock up. I did this while driving a couple days ago with my tranny builder. No other changes were ever made in the wiring in the 10 years that I have owned the car.
 
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v6turbo87

Active Member
Here is what my 87 brake switch looks like. Note all factory style connectors. The pictures above look like somebody cut and spliced things using crimped on connectors

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GNRick

Retired member
Here is what my 87 brake switch looks like. Note all factory style connectors. The pictures above look like somebody cut and spliced things using crimped on connectors

Posted from the TurboBuick.Com mobile app
Has your switch ever been replaced? Your wires/plugs look exactly like mine, but your switch looks like the aftermarket ones sold at the parts stores. Funny thing, the parts stores switches are black, while the GM switch is white. Yours looks like a white after market switch. Of course maybe GM changed the switch and yours is original, who knows.
 

RmvBfrFlght

Well-Known Member
Here is what my 87 brake switch looks like. Note all factory style connectors. The pictures above look like somebody cut and spliced things using crimped on connectors

Thank you for posting the pic, it now makes more sense as to why it has been confusing.

RemoveBeforeFlight
 

RmvBfrFlght

Well-Known Member
Has your switch ever been replaced? Your wires/plugs look exactly like mine, but your switch looks like the aftermarket ones sold at the parts stores. Funny thing, the parts stores switches are black, while the GM switch is white. Yours looks like a white after market switch. Of course maybe GM changed the switch and yours is original, who knows.

With your switches looking like the ones v6turbo87 posted, note the two slightly twisted together pink w/black-strip wires in the lower left area (see his pic). They are going to the upper brake pedal switch. And are the power (+12 V) to the TCC solenoid switch. Check these as they are powered by the ECM/SOL fuse.

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GNRick

Retired member
The cruise works but I'll check the ecm/sol fuse as you say. So rmvbfrflght will you be rewiring your switches this weekend? ;)
 

RmvBfrFlght

Well-Known Member
The cruise works but I'll check the ecm/sol fuse as you say. So rmvbfrflght will you be rewiring your switches this weekend? ;)

:) Not touching the brake/tcc switch as it finally works as is :p. The car doesn't have CC so no issues there. Apparently an older brake/TCC switch assembly was swapped into this car. That better explains the hacked up wiring. Didn't mean to run you down the wrong path, even the TCC wiring diagrams show it's switch paired with the brake switch.

Thanks again v6turbo87 for the picture.

After checking the ECM/SOL fuse check if the PNK/BLK wires have power to them (need to key-on, engine-off). If so, then check the switch adjustment, check that the purple wire at the switch gets +12 volts on it with the pedal at rest. If not then the CC switch assembly is likely bad. Many times these switch assemblies can be opened up, the old grease cleaned out, new grease and reassembled.

Just need to go slow when opening them up as they have a spring inside.

RemoveBeforeFlight
 

GNRick

Retired member
I checked the pink/black wires and they do get power. I don't have a ecm/sol fuse...mine is labeled ecm batt and the owner's manual says it is for carburated cars. I tested two new GM brake switches and neither one appears to send power to the blue plug with the brown and grey wires. I pryed open the top but couldn't figure out what the problem is. There was no grease in it. So I basically gave up and just installed a rocker switch which energizes the brown wire going to the transmission. I can hear the solenoid click clear as day with key on engine off. Haven't taken it for a ride yet but I have another question....if I can hear the solenoid click, then doesn't that mean the solenoid is grounded? I thought the ecm sends the ground signal at about 45 mph?
 
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v6turbo87

Active Member
Lets back up for a second. The brake switch has 2 sets of contacts in it. One is normally open and one is normally closed. The TCC connector is connected to the normally open contacts and the brake light connector to the normally closed set of contacts. With the plunger pushed in--"foot off the brake"--the contacts for the TCC connector are closed and the brake light connector are open. So that means 12 volts to the TCC solenoid and no power to the brake lights.
The brake switch contact DOES NOT send power to the blue TCC connector. One of the wires on the TCC connector gets 12 volts from a fused source, it goes into the switch through the switch contacts and out to the 4 pin connector on the tranny to provide 12 volts to the TCC solenoid. If you want to test the brake switch you use an OHM meter. Disconnect the connectors. Measure across the 2 terminals that the TCC connector is plugged in to and with the plunger NOT pushed in it should read open or high resistance. Push the plunger in and it should read a short or close to 0 ohms. Forget about the other part of the switch for the brake lights--it has nothing to do with the TCC circuit.

Yes, if you apply 12 volts with your toggle switch and you hear the TCC solenoid come on something is wrong. The ECM does provide the ground for lock up.
Put you meter on OHMs and put one probe to ground and put a paper clip or a small piece of wire in Pin F of the ALCL. Touch your other meter lead to the paper clip. It should read open--Key on Engine off OR on. If you read a short/0 ohms then there IS a short somewhere on the ground side of the TCC solenoid.
 

GNRick

Retired member
Which is pin F.....top right of ALDL? Also, a few weeks ago Earl had said to put koeo, lay under the car and press the brake pedal with my hand. If I could hear the solenoid then everything is working as it should. At the time, I was able to hear the solenoid.
 

GNRick

Retired member
V6Turbo87- I tested my brake switch with an ohm meter and it tests as you say. So I guess the brake switch is good. Ok went for a drive. Turned on my rocker switch on hwy. Cruise control works but no lock up. Pulled over on a side street, jumped a wire from port F to A on aldl. Now I have lock up, even with my switch off! I had spliced the rocker switch into the brown wire but didn't actually cut the brown wire. So this appears to mean that 12 volts is now going to transmission, ground wire (tan/black) is good from Transmission to aldl, but not for the part of the wire that goes to the ecm? Assuming the ecm is commanding lock up, the ground is not getting thru. Maybe I'm off on another tangent. Any advice? Should I probe the tan/black wire at the ecm with key off and see if it provides a good ground? Or is this a waste of time since the wire won't ground until the ecm tells it to?
 

v6turbo87

Active Member
If you can force lock up by grounding Pin F of the ALDL then you are correct that a TCC lock up command is not being sent. The problem now is why.....
You can try and monitor Pin F of the ALDL with your meter while driving. Put one probe in Pin A and the other to Pin F with the meter on Ohms. It should read open until the TCC command signal is sent then read a short. You will obviously need to get up to highway speeds when monitoring the meter. Different chips command lock up at different MPH. What chip are you using? I guess it could be a broken wire from the ECM to the TCC solenoid ground side????
 

GNRick

Retired member
Extender chip from Full Throttle. Lock up used to work fine, no changes were made to the chip. Will play with it some more later today. I'll hook up my scan tool and see if the lock up light comes on. Thanks for your help!
 

RmvBfrFlght

Well-Known Member
Note: the blue connector with the gray & brown wire is for the cruise control (CC).

The clear connector with the dual pink/black wires and the purple wire is for the TCC.

Yes, it is connected to the upper switch assembly that has the large vacuum line. Apparently GM switched these up when CC was installed in a vehicle. With no CC, there is only the one switch which is what I posted pictures of.

With CC the picture that V6Turbo87 posted is correct.

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GNRick

Retired member
Here is an update....Checked for power at wire in 4 prong plug at transmission and verified about 12 volts. If brown wire in two wire plug at brake switch is for cc then I don't know why there is 12 volts at transmission now. Hooked up scan tool and went for a ride. At about 45 mph scan tool showed tcc lock up. Touched the brake with right foot on gas and rpm's rose as they should when converter unlocked. Cruise works when I switch on the rocker switch. The rocker switch has no effect on the torque converter. So anyway I don't know what I did but it seems to be fixed, although cruise needs the rocker switch to be on.
 

TurboSmart

Member
I wonder if I removed CC from my car, how I can have tcc?
Also, if my car does not have a lookup converter, could energizing the tcc will damage something?

I dont notice any rpm raise when pressing the pedal over 45 mph.

Any way, other than a rocker switch how we can fool the tcc to engage?

Any damage if I run the car at highway speed with no lockup other than low mpg?
 
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