We just got a great question from a customer. He has his 1972 Chevy truck wired with our 20-Circuit Harness Kit. He has a LS3 engine using the GM ECU to control the engine. The ECU is also managing the torque converter lock-up. Additionally, he has an aftermarket cruise control system. Both the torque converter and the cruise control system need a +12 volt signal when you step on the brake pedal. Our customer wanted to know the easiest way to get this.
One of the advantages of our Infinitybox system is how we connect to your switches. Our inputs are very low-current and just require a ground signal to turn on an input. This means that you can run very light-gauge wires to your switches. It also means, that there is no high-current at the switch, which is safer. Since there is no power at the switch, some guys get confused on how to get 12-volt outputs for things like their torque converter and cruise control systems. This is much easier than it looks.
The ECU or a separate transmission controller is going to control the lock-up solenoid in the torque converter. In higher gears or at specific speeds, the torque converter locks up to improve fuel economy. The ECU or the transmission controller needs a signal to know when you have stepped on the brake so that it will disengage this lock up.
The same thing needs to happen for the cruise control. The cruise control system needs to know when you have stepped on the brake pedal so that it can disengage.
Remember that there is no battery power at the brake pedal switch. You could splice off of the brake pedal output on the rear POWERCELL to get this 12-volt signal for the torque converter and cruise control systems. However, you’d have to run a wire from the back of the car all the way to the front. That goes against one of the basic benefits of our system.
The easiest way to get a +12 volt signal to the torque converter and cruise control systems is to use one of the OPEN outputs on the front POWERCELL. In most systems, output 8 is OPEN. This is the dark-green wire on the output A harness. An OPEN output means that there is no specific function assigned to it. These can be used generically as auxiliary outputs. Connect the OPEN output wire to the ECU and the cruise control systems. Follow their respective wiring diagrams to know where to make these connections.
Take the MASTERCELL input and connect it to the brake pedal switch in the same way that you have wired your brake pedal input. You can have multiple MASTERCELL input wires connected together to one switch. Follow your configuration sheet to get the right MASTERCELL input wire color. In the case of output 8 on the front POWERCELL, this is input 8 which is the blue wire with the light-blue stripe on the MASTERCELL A harness.
When you step on your brake pedal, the MASTERCELL will see two inputs ground together: one for the brake lights and one for the OPEN output on the front POWERCELL. The brake lights will turn on in the back of the car. You will also get +12 volts on the OPEN output on the front POWERCELL. This will send a signal to unlock the torque converter and to disengage the cruise control. When you take your foot off of the brake pedal. the MASTERCELL sees the two inputs turn off. It will send the command to the rear POWERCELL to turn off the brake lights and a command to the front POWERCELL to turn off the OPEN output.
The torque converter and cruise control systems will get their brake pedal signal from the local POWERCELL in the front of the car. This keeps the total amount of wire running through the car to a minimum.
Please contact our team with questions on this post or on any other topics related to wiring your car with our Infinitybox system. Click on this link to get connected to a member of our technical support team.