I have recently purchased three (3) different Bachmann alco s-2 switchers;  one us army (part # above), one sf zebra strip and one sf blue and yellow paint scheme.  two of the units have directional lights, i.e., forward front light on reverse light off, reverse rear light on forward light off.  The third unit the part #63405 us army paint scheme, in forward the front light is one bright and the rear light dimmed and in reverse the rear light is on bright and the forward light is dimmed. 
how do I change the lighting so all three (3 are only front light on in forward and only rear light is on in reverse?  I can change CV's however which ones control this function?

thank you for your anticipated help.