2005 Dodge Ram 1500 4x4 - Intermittent wiper problem

Hi, here is an odd-ball problem I need some help with. My wipers work on the low speed and high speed settings but not on any of the intermittent wiper settings. I have a wiring diagram for my truck but it is not the most helpful in diagnostics. Here is what happens...You can turn the wipers on low and they work. You can turn them to high and they work. Now, if you initially turn them to intermittent, they don't work in any intermittent position. If you switch them from low speed to intermittent, they keep on wiping on slow and will eventually stop. Now based on my wiring diagram, I don't think there is a problem with the motor connections. I am guessing it is either the body control module or the multi-function switch. Does anyone know of a method to determine where the fault is? Thanks a lot. Al