SO, if I'm understanding you correctly, you can no longer press the yellow bypass button to mow in reverse? My first suspicion is that the yellow button may have gone bad internally. What I would do is locate the switch under the tractor that contacts the pedal linkage, move it away from the linkage so it doesnt know you went in reverse. This is a primitive system. That switch on the pedal linkage is the only way the system knows you went into reverse. Don't cut wires, just move the switch. Some systems have a relay in this circuit and we dont want to energize it all the time by twisting wires together. Just move the switch. Never have to mess with that yellow button again. I only suggest this because you already have bypassed your seat switch, so I'm thinking you'll have no issue with making the reverse system defunct. Good luck.