I have a 97 F150 4x4 with the 4.6 engine. having problems with the speeds on the wipers. Replaced the Multifunction switch (Wiper/turn signal) and still no luck. Am being told that it is the GEM unit. Can find the units on line but I am having trouble matching the numbers. Specifically the last 2 letters. The number on my module is F75B-14B205-NC C. Are there other numbers that are interchangable? Some of the on line items show as all models, but when I chack at salvage yards they are looking for specific numbers. In a bit of a bind here,,,,bought this as a project for my son....willl soon be "upside down".

 

Not all GEMs are the same, there are a few models :

 

I chased this problem earlier this year. Long story short, I had ended buying not one but 2 bad multifunction switches from NAPA. Got a Motorcraft mfs from the dealer at twice the cost, but that fixed it. Make sure you have a good switch!!! I chased this, replacing mfs, GEM unit, and wiper motor. At least I could return the mfs, still have GEM and wiper motor in my garage. Wasted money.

 

jump n makes a very good point, I just did the bad thing and assumed testing lead you to the change it.

If you have the old one you took out you can test is easy.