Crown Speed Sensor - Blue/Red wire?

[Dreamkiller]

Hello all,

I have a Crown engine and have managed to wire up everything ok however there is one wire i need to trace which is missing.

Can someone please tell me where the Blue/Red wire that comes off the speed sensor should end up? I have traced this wire to a grey plug which is where it ends.

I have wired Yellow/Red to Ground and the Red/Yellow to +12V so all good with those wires.

Thanks.