The Guest Model 2606 6 amp charger has a fuse located within a yellow capsule near the red alligator clip. If your charger will not go to red then you have probably blown this fuse. You can call Paradigm for a replacement.
The key to using this charger is to place the alligator clips on the battery before you plug it in and then unplug the charger before you remove the clips. You do not want the charger plugged in and the alligator clips unclipped from the battery.
The model 2606A has the reverse polarity protection built in to the charger and does not have the fuse.