I finally got it figured out....
After looking at this page at Utterpower.com:
http://utterpower.com/genhead.htm, I found that my 4 wire gen-head was factory wired for 240V. I was ony pulling 50 amps on one 120V leg.
After switching a couple of wires to the voltage regulator and strapping the leads together, I now have 120V at the full 100 amps.
I should now be better prepared to understand the ST genhead mated to the Listeroid that I will be purchasing very soon....
I plan on having the Listeroid run my 220V airconditioning load using biodiesel next summer. Shoud be interesting...