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99 GMC Suburban brake pedal switch TCC ?

FellowTraveler

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OK: I am at a standstill installing my stand alone trans controller.
The install directions, call for a "brake switch to ground for TCC"
Attached image hopefully is the correct one, circuit 420 "D" terminal is TCC
"so the question is; does it go to ground when pedal is pressed, or?"
 

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JiFaire

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Should be open when brake is pushed, I think... the OBDI mod activated the lock when switched to ground.
 

FellowTraveler

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Should be open when brake is pushed, I think... the OBDI mod activated the lock when switched to ground.
Mine is OBD2 and I forgot, the stand alone controller calls for TCC "unlock" when brake pedal is pressed..may bad for not including that.
 

FellowTraveler

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I called the builder of the controller; he told me that I can not the tcc circuit and have to use a relay to ground tied into brake light circuit to disengage converter when coming to a stop...
 

JayTheCPA

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That should be easy enough if the truck has a brake controller.

Actually, IIRC there is fuse cluster above and to the left of the brake panel which might have a vacant post with 'NAT' above that post. That is where I pulled the signal when I installed a brake controller in the Burb.
 

FellowTraveler

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That should be easy enough if the truck has a brake controller.

Actually, IIRC there is fuse cluster above and to the left of the brake panel which might have a vacant post with 'NAT' above that post. That is where I pulled the signal when I installed a brake controller in the Burb.
I have the additional HD trailer harness...
 

FellowTraveler

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So the TCC requires power to unlock? Seems odd
No, it needs a momentary ground to unlock the TCC, according to the designer the GM brake switch TCC terminal will cause feedback and damage the controller. So I wire a relay to the brake light wire which in turn sends the momentary ground to the controller to unlock it, I have lockup in all 4 gears.
 

ak diesel driver

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So your using the positive brake light power to trigger the relay which in turn is sending ground to the controller?
 

FellowTraveler

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So your using the positive brake light power to trigger the relay which in turn is sending ground to the controller?
Yes, that is what is required.
Also has a momentary switch for tow mode OD.

As I understand it, the GM brake switch TCC terminal is hot and goes to negative when brake is applied when the brake is released it goes hot gain and that destroys the controller I am using.
 
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THEFERMANATOR

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The picture you posted does not look correct. The brake switch has 3 switches inside of it. One is normally open and closes when you press the brake pedal, the one for the tcc signal is normally closed and supplies 12v+ until you depress the brake pedal at which point it goes open. And iirc the other side works the same as the tcc switch, but it is for the shift interlock switch so that you have to press the brake pedal to take it out of gear. If you need one that sends a ground signal when you press the pedal, you will have to do a relay off the brake light switch side.
 

FellowTraveler

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The picture you posted does not look correct. The brake switch has 3 switches inside of it. One is normally open and closes when you press the brake pedal, the one for the tcc signal is normally closed and supplies 12v+ until you depress the brake pedal at which point it goes open. And iirc the other side works the same as the tcc switch, but it is for the shift interlock switch so that you have to press the brake pedal to take it out of gear. If you need one that sends a ground signal when you press the pedal, you will have to do a relay off the brake light switch side.
Thanks FERM, I could not find my shop manuals for this vehicle, so searched the web found many similar switches with different tcc wiring schemes...in the end its a good thing I did not just tie directly into the GM brake switch TCC terminal.
 

FellowTraveler

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I found the terminal for the brake light output at (F6) in the convenience center under dash, also found a short in tthe steering column multi-function switch, hopefully the switch will arrive today...
 

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