On January 18, 1999, approximately 1210 mountain standard time, a Beech E90, N16NM, being operated by Seven Bar Flying Service of Albuquerque, New Mexico, was not damaged when the elevator control cable failed during initial descent into Clovis, New Mexico. The airline transport rated pilot, flight nurse, and patient were not injured. Visual meteorological conditions prevailed, and an IFR flight plan had been filed for the nonscheduled domestic passenger air taxi flight being conducted under Title 14 CFR Part 135. The flight originated in Albuquerque, New Mexico, at 1112. The air ambulance flight was transporting a male infant in an incubator to Clovis, New Mexico. During the descent into Clovis, the control yoke moved to the full forward position. The pilot eased back on the yoke and the nose pitched up. The pilot was able to maintain control by the use of power and elevator trim, and elected to return to Albuquerque, where an uneventful landing was made. Postincident examination disclosed a drooping wire bundle beneath the pilot's seat, at F.S. 122. The insulation around the H16A10 wire (copilot's windshield heat) had chafed against the elevator down cable (part number 50-524439-31), causing a short circuit. Although the pilot did not detect the odor of smoke, the elevator cable was burnt through and had separated. No circuit breakers were opened nor were any fuses blown. Seven Bar Flying Service then grounded its remaining fleet of four E90s for an inspection. No discrepancies were found in three of the airplanes (serial numbers were above LW-156), but some chafing of the electrical cables wqere noted on a fourth airplane, N14NM (s.n. LW-35).