Auxillary Fan

[hartbraker]

I have a question regarding the stock auxillary fan on my 1986 k30.
The fan is still working as I have supplied power to it and it kicks on... the problem is that when plugged into the thermostat/reostat (not sure which one it is) on the passenger side of the 7.4L, there seems to be constant power to the fan. This is a problem because the fan circuit has constant power (even when the truck is off).

SO, my question is, what type of thermostat/reostat should be on the 7.4L and what do I need to replace to get this back in working order?
Currently, there is just a female blade style plug that is connected to what I'm assuming is the wrong thermostat... but I've definitely been know to be wrong. I'll try to get some pictures up asap but would appreciate any input from those of you who are familiar with what I'm talking about.

When I talk to the local parts store, they show a thermostat that has a different style plug that I do not have, which very well could be the case as the PO liked to cobble wiring! (BIGGEST PET PEVE)... there is only one wire leading to the current blade style plug in. Digging deep here as I've not seen many of the factory auxillary fans on these trucks, but then again I'm a youngen... so I haven't worked on too many of em besides the 5 my family has owned.

HELP GUYS
Thanks in advanced!