Steve, no I didn't know you had the automotive electrical experience.

I'm off to download some spice application and SIM this... or should I just contact a local PCB house and get them to send me a prototype... afterall if its wrong I'll bin that one and order another

Any chance of a quick schematic on the input.. I was planning on using a small 100mA 5v reg for the PICs supply, and assume that the transistor would be between +5 and gnd (C and E) with the base connected to the sensor ?