Mownie - Your posts are fantastic. Thanks. I do have the JD manual but as you say, the schematics are not great. I do have the seat switch unmounted so no frame short there. Pink wire doesn't seem to be the problem - fuse blows with X3 and X4 connectors connected (ignition on, seat switch depressed, and all other components and switches disconnected) but does not blow when X4 disconnected and pink wire 800 isolated and connected alone to its post on IM. It's odd that with X3 connected, no individual wire in X4 will cause the fuse to blow, but when all the wires in X4 are plugged in, the fuse will blow when the ignition is on and the seat switch is depressed (and all other components and switches disconnected). Makes me think the IM is bad but I'm still not sure. Also, I did find that if X3 connected and X4 disconnected, connecting yellow-black wire 410 in X4 to its post on IM will cause fuse to blow (again with ignition on, seat switch depressed, and all other components and switches disconnected). 410 goes to ground. Again this makes me think the IM is bad. Also, I'm not sure how IMs go bad. I was just mowing the lawn, hit a bit of a bump (nothing unusual) and the tractor just shut down. I guess it's just as likely that a circuit board just dies as some other components. I figure a wire shorted due to a physical abrasion or corrosion would more likely be somewhat intermittent while my problem is not at all intermittent. Any additional thoughts before I replace the IM?

The A/C relay on your Honda, like most vehicles today, is computer controlled. The relay will have electrical power at two terminals of the relay with the key on and power at only one terminal with the key off. If there is no electrical power present at the relay, then you have to inspect the fuses. There are two fuses for the relay. One can be found in the under dash fuse panel. It will be a 7.5 amp fuse and will be located in position #6 of the fuse panel labeled A/C clutch relay/cooling fan relay. The other fuse is located in the under hood relay and fuse box. This is a 15 amp fuse and will be in position # 34 and labeled condenser/fan. If both fuses are good and there is electrical power to two of the terminals at the A/C compressor clutch relay, then you have a control problem. It could be as simple as a bad relay or the A/C system is low in charge. The A/C system has a pressure switch that stops the operation of the A/C compressor if the charge of refrigerant in the system becomes inadequate, too low. This is done to prevent damage to the compressor. To diagnose a control problem will require more specialized equipment, higher level of training and knowledge for diagnosis. At this point I would suggest that you involve a repair facility to perform this diagnosis.

Or a T-Stat wiring issue, such as your "B"'s and "C"'s mixed up between stat, indoor unit and outdoor unit

Well, it seems that the blue wire is not what you expected if the fuse no longer blows. Normally the temperature has to reach the next degree increment to turn off. I have seen several brands that work like this. I have never seen a Ch and Cc. It seems to be an additional setting for the stat. Are you sure it needs to be jumpered? This could affect the stat if done wrong. I have seen blue used as a chassis ground, which would explain the fuse blowing. Check the battery for voltage, if low it will affect the thermostat. Some stats are very temperamental with low voltage. If the color wires are nominal, green should run the fan. One wire jumpered to the red wire should run the fan, after the delay ends. If you jumper grounf you will blow the fuse. Check at the furnace end for where the wires connect. If the green is connected to G, then this would be correct. What kind of ventillation control?