I have a dimmer unit for a fan I built for maybe 10 bucks I'll post a pic for you tommorrow but heres how its made. get a two receptacle box and a dimmer and 15 amp at least receptacle and a 3 conductor power cord. ground from the power cord goes to the receptacle ground connection and 1 of the hot wires goes in to 1 connection of the dimmer unit and the other goes to one of the sides on the receptacle. then the other coming out of the dimmer just goes to the last receptacle connection. mine works great I use it with one of those bathroom exaust fans that also has a power cord wired in. the fan was like another 10 bucks at home depot. the fan also has a 3" exaust that hooks right up to the 3" ducting. but are you running 12v fans? if so go to an auto parts store and just get an old fashioned heater switch and use that inline with your 12v hot lead to your motor because it is made to run on 12v and will have 3 speed settings. but I think my way is cleaner and the fan just plugs in like its being plugged into the wall. it sounds like you just need to get a normal light dimmer and dont mess with cieling fan ones. normal ones only have two wires