Went to sell my MinnKota Endura c2 Transom mount trolling motor. When l last used it 6 months ago it worked fine. Met the buyer we hooked it to the battery it only ran in one speed? Hooked it up to his truck while it was running, same thing one speed only. Is there some kind of safe mode on these things that it's only running in one speed while it's not in the water? Or did this thing just die sisitting in my garage the last 5 months? Of course the gentleman that drove an hr to meet me thinks I tried to sell him a motor that didn't work and I'm sure is on his way home to assault me on the group he saw my motor for sale on.

Could have been a lack of power running it off of a running truck battery.  Sounds like it didn't have enough juice to satisfy the power threshold on the higher gears to me but I could be wrong.  Try it with a full battery when the vehicle isn't drawing on the current and see if that works.  

I would say dust or water got into your switch contacts.

It should still switch speeds despite how low of power it's getting, granted it won't be turning very fast, but there should still be a difference. Check the switch and test it out next time before you go to sell it. 

If you hook it up backwards it will only run one speed... maybe you accidentally put it on the wrong terminals