Electric diff lock experiment

[Tony Lum]

Hi gang,

On Saturday, I had clear access to a '86 4kq in the local pick and pull 
yard and I was able to pull both front and rear diff lock servos.  I've 
always wanted to pull the diff lock panel in my urq to put a gauge package 
there so that means relocating the switch.  That's exactly not straight 
forward process as the vacuum switch is a integral part of the panel.  My 
thought was to use two of the 2 way vacuum solenoids that control the 
recirc flap on T85 cars (heater valves on T43 cars) so I could place an 
electrical switch control anywhere I wanted.  I found the switch I wanted 
at the local Pep Boys.  I think its made to be a old style head light 
switch.  Two position pull switch just like the original vacuum with strong 
detents and plenty of wiring options.  Mounts with a single 3/8" hole. The 
urq's knob even screws onto the switch without mods.

To make sure the system works, I did a mock up of the proposed system on 
kitchen table using a single 2 way solenoid and made an unpleasant 
discovery.  I first set up the off condition of the switch, i.e. the full 
in position.  Worked great with a hand vacuum pump.  The servo was fully 
extended and rock solid.  Then I switched the solenoid-and nothing 
happened!  I heard the click and my gauge was still indicating 22 in. 
Hg.  WTH was wrong?  It finally dawned on me that unless the other side 
vents, the servo won't be able to switch states!  A close examination of 
the original switch confirms this theory.  That is, when one side of the 
servo is active, the other side is vented to prevent interference with the 
"active" side.  I still think it will work, but it will now take four of 
the 2 way solenoids instead of just 2 as I hoped.

The journey continues...

-Tony
ur-quattro #900302