need info on relay

[edin355]

I recently purchased a 72 swb Ac truck.Im in the process of redoing some of the wiring.Ac cabs are new to me.Next to the horn relay under the dash in another relay with a red,blue,black,andb/w wires. They run into the engine compartment about two foot long and then they were cut off.I have searched books with wiring diagrams but cant find anything showint this relay.Im almost sure it has to do with the ac.I would think maybe it was cut from the wiring hub where the main wires are joined,but dont know for sure. Any help would be greatly appreciated. Thanks for any help. edin 355