Hi Bob can you please post a pic of both the pickups and wires ? I presume this is a SG-1 build. Wire colours from the factory vary so don't assume yellow is neck pup and red is bridge pup. Usually the neck pup will have a longer wire than the bridge pup. Also check the resistance of each pup if you have a multimeter generally the bridge pup will have a higher resistance.
By fatter base I presume you mean the pickup surround ? The factory could have mixed these up too. the thicker surround is for the bridge pup and thinner for the neck pup.