3 or 4 wires to/from pressure sensor?

["Graydon D. Stuckey" <graydon@apollo.gmi.edu>]

On Tue, 14 May 1996, Peter Wales wrote:

> Don't put a voltage divider in the output of the pressure sensor. It will
> advance the ignition and cause you problems as the boost comes up. If you
> want to do it at low cost use a 4.3v zener and a 470ohm resistor.

OK, that's reasonable...

> There are 3 wires coming from the pressure sensor, 0v 5v and output. Use
> your meter to see which is which. The output should be about 2-2.5 v with
> the ignition on and the engine off.

Here's where mine differs.  I have an '86 5KCSTQ, and my MAC-11 has 4 
wires going to/from the pressure sensor.  Also, when I put my digital 
voltmeter on each of these four wires, I saw no voltage at all on any of 
them.  This is too weird, so I concede that I may have screwed up the 
measurement.  But, why do I have 4 wires, when everyone says I should 
have 3 wires?

Thanks.

Later,								
Graydon D. Stuckey								
graydon@apollo.gmi.edu								
Flint, Michigan   USA
'86 Audi 5000 CS Turbo Quattro, GDS Racing Stage II