Honda S2000 start button

The Infinitybox CAN bus system provides an elegant keyless ignition solution especially when deploying the popular Honda S2000 start button switch.

Infinitybox separates vehicle security from the engine start function. This means that doors can be electronically locked and the engine disabled without reference to any ignition key. The inLink key fob performs these security tasks so the only key we’ll actually need is the fuel cap lock (unless we elect to just keep this unlocked). Backup door and trunk keys provide a mechanical way of entering the vehicle if there is no power.

A quick press of the S2000 start button turns on accessory power — that is, switched 12 volts — and holding the button down for about a second cranks the engine. When the button is released, the engine starts up and there is full 12-volt power.

Hacking the S2000

The S2000 switch has five wire leads and Infinitybox only requires two of them to trigger all the power and engine start features. However, it is possible to hack the switch so that separate illumination can be used either triggered by parking lights for night viewing or by switched ignition to indicate that the engine is running.

The hack involves separating the pin 4-5 circuit from the pin 2-3 circuit.

S2000 circuit board hack

A jumper wire was soldered from pin 2 (pins 1 and 2 have only short traces and do not connect with circuit board components) to the area near the circular black illumination element. Pin 3 is the illumination ground.

Close up of trace cut on pin 4

The procedure also requires cutting the pin 4 trace so that the light which requires 12 volts is segregated from the Mastercell input (Mastercell cannot have any 12 volt inputs). Careful scraping with an X-Acto blade first removed the turquoise protective covering and then the copper trace itself.

To validate effectiveness of the circuit board surgery, a voltmeter and bench power supply performed three tests.

  1. confirmation that the small circular light goes on with 12 volts
  2. connectivity validation measured by close to zero resistance when the start button pressed (pin 4-5 circuit operational)
  3. verification that no voltage from the light circuit leaks over into the Mastercell signal

Confirmation of light operation

The S2000 illumination is obviously not very bright but it is sufficient to highlight a ring around the red button. During daylight this may not be noticed, one reason why linking the light to the parking/running lights may make sense. Note that the amperage draw as indicated on the power supply is extremely low.

Pressing the start button to verify switch functionality