8HP Basics: Chapter 2 - TCU Wiring

7 days ago

6 min read

Most "tune" problems on a fresh 8HP install are really power, CAN bus or input scaling problems. This guide covers the wiring and configuration basics for the three controllers we sell; Turbolamik, CANTCU and MaxxECU. This is a starting point for understanding how it all works at a coarse level, so it can become less intimidating and easy to understand.

CAN bus

All three controllers can communicate over CAN bus to the rest of the car, and most integration problems I see are CAN wiring problems. Think of the CAN "bus" as a tree trunk, each tree limb connects to a single module, and the top and bottom of the tree trunk have a resisitor (120 Ohm).

Legit Tip: A common issue is wiring the CAN bus like a spider web, instead of a tree.

CAN bus signals often provide the TCU with engine information to calcuate torque from, like MAP, TPS and RPM. It is also often used to send back data; like cut and blip requests. With OEM vehicle presets, often signals like brake and paddles are also being broadcast onto the CAN bus. By using CAN to communicate signals, a car can save massive weight and complication by simplifying the harness. Think about if the car needed its own wire for every signal. Now you know why 90's cars are electrical nightmares!

The ECU, TCU, and everything inbetween, all talk on the same CAN bus; the "tree trunk". It is a twisted pair of wires referred to as CAN high and CAN low. CAN needs to have 120-ohm terminating resistors at each end of the bus between these wires to provide the correct resistance for the CAN signals to travel up and down the bus coherently.

Each of these modules sends and receives data on the CAN bus. Each modules logic is programmed to only look for the data they need, and ignore the rest. That's why your Shifter will ignore a request from the TCU to the ECU to cut or blip, for example.

Some modules have selectable or integrated resistors in their CAN circuitry. In this case, they can be used at either end of the CAN bus, instead of a seperate resistor. MaxxECU and LINK ECU are examples of this.

CAN Tips

Terminate both ends: To check bus, measure for 60 ohms between CAN high and CAN low. A 120 ohm result means one end is missing its resistor; much lower than 60 means there are extra terminations on the bus, and a resistor needs to be removed. Mare sure modules with internal resistors are onyl placed on the far ends of the CAN bus.
Twist the wires: Run CAN high and low wires as a twisted pair. never use untwisted wires. 22 gauge is plenty. Legit tip: use a drill to twist the wires.
Remove CAN bus bloat: Turn off default module output messages that aren't being used.
MaxxECU Termination: If you are using a MaxxECU as a ECU and TCU (not our MaxxECU Transmission Control Bundle), the MaxxECU has an internal resistor, so put it on one end of the bus.

Example of a twisted pair of wires:

The "Short Bus"

To make CAN wiring easier, we developed our "Short-Bus" CAN Bus. This compact module allows you to connect up to six CAN devices in one central location, eliminating the need to splice multiple modules into a single wire. It features removable 120-ohm terminating resistors at both ends of the bus, making it easy to configure proper termination for your setup. The Short-Bus simplifies wiring, allows you to integrate up to 6 modules per module, keeps everything organized, and takes much of the guesswork out of building a reliable CAN network.

CAN, by Controller

CANTCU: Has three CAN buses. CAN1 and CAN2 talk to the transmission, and CAN3 is for the ECU and the rest of the car. CAN1 and CAN2 have 120-ohm terminating resistors built in; CAN3 doesn't. With Race+, only CAN1 is needed for the transmission. Most shifters connect to CAN3, though some use CAN1 when the native shifter to the transmission is used.
Turbolamik: Has two CAN buses: CAN1 for the shifter, and CAN2 for the engine ECU and rest of car. Turbolamik doesn't control the transmission over CAN; the solenoids and sensors are hardwired to the TCU.
MaxxECU: The 8HP internal TCU's CAN high and low go straight onto the main CAN bus, alongside the shifter, your MaxxECU and any other accessories you have. Check MaxxECU's list of known CAN conflicts before adding other devices.

CANTCU CAN Preset Selection:

Turbolamik CAN Preset Selection:

MaxxECU CAN Inputs:

Power Basics

CANTCU

CANTCU +12V supply: Main supply and ground, with a 10A fuse recommended. It can share ECU or ignition power trigger.
Transmission +12V: A 15A fused +12V supply. On the older OEM and OEM+ software, run it through a time-delay relay, so the transmission stays powered for about 45 to 60 seconds after you switch off the ignition/CANTCU. That gives it time to save its adaptations and go to sleep.
Race+ Update: With Race+, no time-delay relay is needed, because adaptations are saved during normal operation. CANformance recommends running CANTCU and the transmission from the same switched supply in this case.

Turbolamik

Transmission +12V: Constant power, straight from the battery through a 20A fuse or battery safety switch. This must never drop out with the ignition. It keeps Park unlocked if the ignition is switched off while the car is moving, and the TCU saves its adaptations when ignition 12v is removed, but this power supply is still on. Cut that power before it sleeps, and the adaptations aren't saved either.
Ignition +12V: A wakeup signal that switches the TCU, OEM shifter, and LCD display on. It should always turn off before battery power is ever cut, so the TCU can save its adaptations.

MaxxECU

Transmission +12V: A 20A fused supply, direct to the battery or through a battery safety switch.
Transmission Wake-up: A 12V ignition signal, which can share the main ECU power source.
Power-up Order: Main power must be on continuously, or for at least 10 to 15 seconds, before the wake-up signal arrives (at the same time as ECU power on). Otherwise part of the TCU program doesn't initialize, and the paddles won't work in manual mode. Wiring the main transmission power and wake-up power together in parallel is the usual cause of dead paddles.

Digital and Analog Input Basics

Digital and analog inputs usually carry the signals that might not be on the CAN bus, like the brake signal, buttons and paddles, via a physical wire. Get the brake setup wrong and the box won't go into gear. Some of the signals below can also come in over CAN; if they do, you don't need to wire them to the TCU.

Digital inputs are a yes/no signal. They're most commonly triggered by a ground, which makes wiring a switch simple: Connect one side of the switch to chassis (Ground), and the other side to the TCU input.

Analog inputs are usually variable signals ranging from 0-5V so they can be mapped into an value instead of just "yes" or "no". They're most often used for things like throttle position and clutch position. In some cases they're used for the brake switch, via tapping into existing +12V hot brake light wiring, as well.

Commonly Used Inputs

Foot brake: Analog input, acting as a yes/no switch. It can also be ground-switched on a digital input, but that's less common. Also can be via pressure threshold logic i.e. 75PSI or more = Brake On.
Paddles: Digital inputs, switched to ground.
Mode Switch: A digital input, commonly used with paddles when you're running the car without a CAN keypad or OEM shifter.
Throttle Position: If it's not on CAN, tap into the existing sensor signal, or add a TPS.
Clutch Position or Pressure: Connect a potentiometer on the clutch pedal, or a clutch emulator that uses a pressure sensor.
MAP Sensor: A 0-5V analog input range. Used on naturally aspirated cars that don't already have one, we usually use this MAP sensor.

Turbolamik Foot Brake Mapping Example:

Turbolamik Clutch Input Mapping Example:

Example of CANTCU Clutch input:

Example of CANTCU Paddle Input Setup:

Example of MaxxECU Virtual Clutch Mapping:

RPM Signal Basics

One of the most important signals a transmission controller needs is engine RPM. Modern ECUs typically broadcast this information digitally over CAN bus, allowing the TCU to receive accurate engine speed data without needing a dedicated RPM wire.

Older vehicles, especially classic muscle cars and vehicles running traditional ignition systems, often use an analog-style tachometer signal instead. These are commonly pulsed signals, such as a 0–5V or 0–12V square wave, with the frequency increasing as engine RPM rises. Depending on the ignition system, the signal might come from an ECU tach output, ignition module, distributor, or the negative terminal of an ignition coil.

Here's how each module can receive an RPM signal when its not available on CAN bus.

Turbolamik: The analog harness has a dedicated engine speed input that can be scaled to suit the signal going to your tachometer.
MaxxECU: Use the trigger input and a crank or cam sensor to reference an RPM calibration. See MaxxECU's trigger examples.
CANTCU: Doesn't currently take RPM through an analog or digital input, so it needs RPM over CAN. That's a big reason carbureted builds go on Turbolamik.

Example of Turbolamik Analog RPM Input Mapping:

Legit tip: Whatever the controller, compare the TCU's engine RPM to the ECU's or the tach while revving in neutral. If they don't match, fix that before you tune anything.