john deer L100 dies when i let off the brake in reverse. PTO is off.

im a john deer technician for south texas implements, tractor city and im working on a customers L100 lawn mower and as I put the unit in reverse with the PTO off the engine dies. unit acts as if the PTO is on. ive checked all the RIO and RIS sensors and the PTO and brake sensors. all are in normal working condition and have continuity. is there and other sensors or relays im not checking or is there a further electrical problem for this unit?