rpm signal wire

hi all,
can anyone help me find the rpm feed from the engine, i need a rpm signal for my lpg.
the car is a 1995 4.6 p38 rr
many thanks

RPM signal is fed to the Rev Counter from the BeCM which recieves the tacho signal from the Engine ECU - 4 pulses per revolution....

The Classics used a 'W' wire from the alternator for the Rev Signal and the ECU used a pulse from the LT side of the Coil, each time it fired it sent a pulse to the Engine ECU to tell it it was still running!! - I haven't seen such a reference on the P38....

As attached from RAVE...