Torque Converter lock up

[67Steven]

Originally Posted by dayj1

Correct, 87A should be grounded. While the relay will work as shown (with 87a grounded), I'd scrap it all together. On a Gen IV ECM, you can just run the TCC lockup signal wire (purple in the diagram) directly to the wire going to the brake lights (blue in the diagram). No need for a relay and it does the same thing with no extra parts.

Okay, I am now confused (not hard to do) I just went out and checked, the brake light side of the switch does not ground when brake is off, so how does the TCC have a ground just hooked to the brake light feed?

Wouldn't the above diagram be exactly the same as just running the TCC wire directly to the brake light wire? If the TCC in fact needs to have a ground when not on, it does need a relay to produce that, doesn't it?

Or am I not thinking through this correctly?

[Andy4639]

I don't know if mine fall's under this but my 4l80e transmission with a 2001 ECU has the cruise controll brake switch hooked to it and it works fine. Shifts good and downshifts fine. Locks and unlocks as it's suppose to.
Here is a typical relay hook up for 12 volts +.

[Hart_Rod]

Originally Posted by 67Steven

Okay, I am now confused (not hard to do) I just went out and checked, the brake light side of the switch does not ground when brake is off, so how does the TCC have a ground just hooked to the brake light feed?

Wouldn't the above diagram be exactly the same as just running the TCC wire directly to the brake light wire? If the TCC in fact needs to have a ground when not on, it does need a relay to produce that, doesn't it?

Or am I not thinking through this correctly?

It grounds through the tail light.

Originally Posted by Andy4639

I don't know if mine fall's under this but my 4l80e transmission with a 2001 ECU has the cruise controll brake switch hooked to it and it works fine. Shifts good and downshifts fine. Locks and unlocks as it's suppose to.
Here is a typical relay hook up for 12 volts +.

Andy - 6L80 TCC are wired differently than the 4L80s.

[Andy4639]

OK I thought so but after reading all this I just wanted to make sure.

[dayj1]

Originally Posted by 67Steven

so how does the TCC have a ground just hooked to the brake light feed?

The filament in the tail light bulb acts as a pull-down resistor to ground. That's why a resistor needs to be added into the circuit if/when you run LED tail lights (because an LED has no filament and does not allow current to flow backwards through it).

[67Steven]

Originally Posted by dayj1

The filament in the tail light bulb acts as a pull-down resistor to ground. That's why a resistor needs to be added into the circuit if/when you run LED tail lights (because an LED has no filament and does not allow current to flow backwards through it).

Ahh, now I see. Thanks.

So would the TCC not having a ground cause my problem of a binding feel after driving for a while? This post here http://67-72chevytrucks.com/vboard/s...1&postcount=13