When the ignition is turned on, the fuel pump starts for a couple of seconds to build up the fuel pressure and then stops again, if the car starts as it should the fuel relay detects the tacho signal (engine is running) and starts the fuel pump. This to prevent the fuel pump to deliver any fuel when the engine isn't running, don't want any fuel if you have crashed the car, would you?
The original tacho signal is fetched from the Bosch ignition system ( at least on my car from 1985 ) and are used both for fuel relay to detect that the engine is running and tachometer. If one removes the original Bosch ignition, one must replace the tacho signal also otherwise the fuelpump will never start due to missing tacho signal.
The good news is that Megasquirt has a 12V sqare wave tacho signal out of the box. The only thing to do is to remove the cord from the Bosch system and replace it with the one from the relayboard. Works perfect without any modifications. You can see the purple cord connected to the green/yellow cord which is the one going to the fuel relay and tachometer, the red (not used) cord is the 12V supply earlier used by the Bosch system.
