Rear thermostat blows fuse

[Soundchaser]

I have a 2012 Fuzion 310 toyhauler. It has two thermostats and two a/c units. The fuse in the garage thermostat (the actual thermostat, not on the panel) blows on the second thermostat whenever I try to run the heater. The heater works fine on the first unit, and the A/C and fans work on both units. It is only when I try to run the heater on the second thermostat that it blows the fuse. (and the front unit continues to run fine) I bought the unit used and did not check the rear thermostat for heating so I don't know if this is a new problem or not.

I figure I have a short to ground but have a couple of questions. I assume the wiring from the first and second thermostat terminate at the same place on the furnace, so shouldn't the second first thermostat shut off when the second does. Also, both thermostats look exactly the same, but the fuse in the rear thermostat is a different size (shorter in length) with a slightly lower rating. The fuse holder is shorter, it is not because an incorrect fuse was used.

Thanks!

[travelin texans]

Unless both the units are equipped with heat pumps only one should control heat as there's only one furnace. If I were guessing the t-stat in the rear will not control the furnace. If it's a heat pump it would control that & would produce heat til the outside temps got down to 38-40 degrees then only cold air.
The front t-stat if a heat pump should operate as a heat pump til the temp inside drops 3-5 degrees below t-stat set temp then furnace should fire up. With no heat pump the furnace should start up.

[ctbruce]

A second furnace or heater is probably just a heat strip. It will be inside of the air conditioner unit underneath the cover. You'll have to pull the cover off and look and see. It will be towards the front and have fins. On mine it plugged in on the side. If you do a YouTube search you will probably find some additional information on it. It is not connected to the main furnace in any way.