[LightningGSX]

The park-neutral input(clutch input) into the ECU is a high impedance input with an internal pullup resistor to power, meaning it rests at a logic 1(on) and it takes very little current to switch from 1 to 0 or vice versa.When the clutch switch is activated(clutch depressed) it grounds(logic 0) its signal output.Without the diodes, even when the clutch is pressed, and it grounds its signal wire, there will still be a logic 1 at the ECU input due to power through the starter relay coil.So essentially the 12v power applied to one side of the relays' coil, drowns out the ground signal from the clutch switch.If you take a high impedance test light and probe your added clutch wire, you'll see exactly what I'm talking about.