Lights quit working

Look under the loco and make sure none of the wires came out and got chewed up in the gears(diesel). This happened to my new Alco S2 back in april. Beacon light wires fell out on the gear of the rear truck and was sawed through. I believe there is a feature reset with a MTH transformer.

Others will be by with suggestions.

I have checked all of the wires and connections.  All is good.  

I will check with a local HS and see if they can reset it.  What would cause it to malfunction?  Thank you

It's one of those twilight zone events.  You are not the only one that has reported this.

Your LHS should be able to do a Feature Reset using a conventional transformer that has the Whistle and Bell buttons.  You basically pressing the Whistle Button once followed by the Bell Button 5 times.  They'll know what this means.  The engine will toot twice and the lights should come right back on.  Maybe 1 minute elapsed time.

If for whatever reason this does not work, they need to perform a Factory Reset which requires the DCS-TIU system.  This is a bit more involved but maybe 5-10 minutes elapsed time.  In this case be sure to mention you will be using the engine with the DCS Remote Commander; they'll know what this means if they sell MTH stuff.