Sears tractor dies when blades engaged???

I have a Sears 23 HP (Koehler)(917.275041) garden tractor. When I engage the blades by pulling out on the PTO switch, the engine dies suddenly (just like turning the key off).

Without the PTO switch being pulled/blades engaged, everything runs very well. If I start the tractor, and then remove the PTO switch and place a jumper between the 'hot' and the wire to the electric clutch, the blades engage and everything works fine.

looking down into FEMALE PTO PLUG: (jumper X to X)

_(1)___ ..... _X(Hot)_ ..... ___(3)___
__(4)__ ..... _(5)____ ..... ___(6)___
............. ___(7)___ ......X(el. clutch)

I have replaced the PTO switch. No change. I have also replaced the Relay Assembly. No Change. The fuse (30 amp) near the battery is good. I have TEMPORARILY bypassed the seat safety switch, and the brake pedal safety switch, both with no change .

Any suggestions are greatly appreciated!

Jim S.
July 2010