Courtesy Light Circuit Issue

[scarecrow]

Brought some little halogen globes from Jaycar (small 15w bayonet 12VDC ones) with the intention of having them light up the footwells as extra courtesy lights (I can't afford cathodes/neons). Got to the two wires which send the "door open" signal (they were wrapped in tape, in fact all the wiring in my car is either heatshrinked or electrical taped, there's no colour!), stripped them back and stuck my multimeter on them. Doors closed they read 0volts as expected, passenger door open they read ~12v as expected, passenger and driver open also 12v, but with the drivers door just open it only reads 2volts.

Wierd.

To get to these wires I took off the driver footsill, pulled back some carpet (directly under where the door sensor is). I assume these are the correct wires (it would help if I could find them closer to the dash, but I can't) but i'm confused as to why they produce different voltage readings.

The electrical wiring manual is no help to me.

Have I got the right wires? Is there another set closer?