What I have found (birth location not verified with documentation) however the dates match his headstone.
David Ehrhardt Birth 6 Dec 1832 in Kassel Westphalia, Prussia, Germany Death 6 Nov 1885 in Klein, TX
I located the following and have posted it on his memorial:
"Captain Horace Haldeman's 4th Texas Field Battery, including the following:
Richard Haude* (corporal) David Ehrhardt ..." -- "The Settlers along Spring and Cypress Creeks face the Civil War" by Diana Lynn Severance, Ph.D
Excerpted from "Deep Roots, Strong Branches: A History of the Klein Family and the Klein Community, 1840-1940" By Diana Severance:
"David Ehrhardt a farmer and cattle rancher who owned 320 acres in what became the Bammel Community on FM 1960, was plowing his fields with his oxen when the conscriptors came to enlist him in the Confederate Army. His wife Elizabeth had to finish plowing the fields alone." -- page 37