You ought to be able to buy a fan relay from wherever you bought the fan(s). Take (+) off the lead to the fan clutch to (+) side of relay and then ground the (-)leg of the relay. Run a (+) from a good source to the Common terminal and then one from normally open to the fan. For a good source I ran a #10 wire from the battery terminal nut to a automotive style breaker mounted on the fender well. You will probably need 20 or 30 amps depending on the fan.
This worked on my 55 F100 so it ought to work on the Dodge.
This worked on my 55 F100 so it ought to work on the Dodge.