I have a 2010 ultra classic and when I try to charge it on my battery tender charger the amber light just flashes I know the charger works because I can charge my dyna but the ultra will not take a charge the battery is only 6 months old and starts with no problem ,and I wouldn't know there was a problem until I realized it won't take a charge

 

I had the same problem... here's what I did:
Pull the seat
Trace the pigtail and find the fuse holder... replaced the 7.5 with a 10amp...
Wash, Rinse, Repeat if necessary...

 

Could be a poor connection. Is is easy to drop a volt or two and that is enough to trip the logic in the tender and cause the flashing amber.

 

Check the fuse on the tender leads...... it could also be a bad tender cable. If you have a meter, check for 12 volts at the connector on the bike. I had to replace the lead on my wife's bike last year because the cable was bad.

 

Check to be sure you are connecting the tender correctly. + to + and - to -...