As per the chart listed above, I installed a 47ohm resistor inline with the sender lead and a good ground. The result was a solid .9 bar on the gauge- just where it's supposed to be! It was a bad sender out of the box!
I contacted the parts vendor (***************) and they are promptly sending a new sender- no questions asked.
Thanks to all and especially Arthur Dalton for helping me though this!

Still wondering why the cluster won't enter it's diagnostic mode though.

__________________
Paul Hansen

1997 S500 (100,000mi)