Grand Caravan auto-stick problems

I have a '99 Grand Caravan, 3.8L, auto-stick on the column.

Symptoms are as follows:
-If I shift into auto-stick mode at any speed, there is no perceptible
change anywhere--gear indicator stays on 'D', no change in gears, etc (this
could be normal, as it has never worked so I'm not sure how it should behave
when first engaged)
-Once in auto-stick mode, clicking the up or down switch causes no
perceptible change...gear indicator stays on 'D', the gears do not change
-The overdrive button at the end of the shift lever also does not work--it
does not disable overdrive at any speed

My Chilton's guide has no auto-stick info at all, nor is it included in the
wiring diagrams, so I'm not sure where to start--can't find a fuse or relay
for auto-stick, and I don't know where the common failure points are.

If anyone has any suggestions or info I'd be much obilged.