ZT 1844 dies when control arms or blades engaged.

[Charley B.]

Bought this one in a basket. Replaced the 18 h.p. Kohler with a 17 h.p. Briggs. Motor runs fine but when the control arms are moved in to operating position the engine dies. Tied off the switches at control arms; motor will continue running but no power to wheels. Also when blades switch is turned on engine dies. Any help and advice would be appreciated.