The Mercury2 controllers can be tied into existing OEM sensor circuits. There are a few rules around this to ensure that both systems operate correctly and is not damaged. It varies for the different products and sensors.

Controllers that share a sensor, has to share a common earth connection. Differences in earth will have an effect on the sensors signal. So make sure you connect the Mercury2 earth to the OEM earth.

Never connect the reference voltage of the Mercury2 to any wire of the OEM sensor. Only the signal wire is connected. It may damage either controller. The sensor already has power or reference voltage from the OEM controller. See the drawings below.

Isolate the Mercury2 wires that are not used. They will have power on them and may short circuit damaging the harness.

If the OEM sensor is not screened it is best to tie in close to the sensor and use the Spitronics screened harness. It may reduce some interference from coils. Remember Mercury2 inputs need to cater for all kinds of sensors and cannot cater for week signals with interference. If you still have interference, then you may add a 100uF and 100nF cap as filtering on their reference line and the Mercury2 sensor earth. See drawings below on Mercury2 Tap-in Sensor filtering. NB. Do make sure which line is signal and which is reference. Crank the engine and measure AC volts to ground of each point on the sensor. The one with the highest value will be the signal line. For speed sensor you may need to lift the wheels up to simulate pulses. It must detect speed at speeds from about 3 Km/H.

The blue Reference volts comes from the OEM controller and it differs between car manufacturers. Some use earth as a reference, other 2.4 volt, 5 volts and even 12 volts. The Mercury2 has isolating capacitors built in to connect to these signals without having a problem with different voltage levels. Mercury2 use a reference voltage for its sensors as ground. Note that Mercury2 requires a minimum 0.5-volt peak to peak signal to function correctly.

Below are the basic connections. Some cars may have a magnetic Crank or RPM sensor in combination with a Hall Cam or Speed sensor. Connect them accordingly. All the Mercury P1 connectors has the same pattern for Crank or RPM and Cam or Speed signals. Note that harness colours differ and should be verified on drawings or GP Priority charts.

For sensor Tap-In conecttions look at the following drawings.

Speed Sensor Wiring
RPM Sensor Wiring MTWX02-2
RPM Sensor Wiring MTSX02-2